Jim Thomson Senior Principal Oceanographer Professor, Civil and Environmental Engineering jthomson@apl.washington.edu Phone 206-616-0858 |
Research Interests
Environmental Fluid Mechanics, Ocean Surface Waves, Marine Renewable Energy (tidal and wave), Coastal and Nearshore Processes, Ocean Instrumentation
Biosketch
Dr. Thomson studies waves, currents, and turbulence by combining field observations and remote sensing techniques
Education
B.A. Physics, Middlebury College, 2000
Ph.D. Physical Oceanography, MIT/WHOI, 2006
Projects
Persistent Measurements of Surface Waves in Landfast Ice Using Fiber Optic Telecommunication Cables The high-resolution data collected during this research will help address fundamental questions about wave attenuation in landfast ice and breakup. The research is motivated by two questions: (1) What is the spatial and temporal variability of wave attenuation in landfast sea ice? (2) What drives landfast breakup? (Collaborative research with M. Smith, WHOI) |
30 Aug 2023
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Hurricane Coastal Impacts APL-UW scientists are collaborating with 10 research teams to tackle the National Oceanographic Partnership Program (NOPP) project goals: to enable better understanding and predictive ability of hurricane impacts, to serve and protect coastal communities. The APL-UW team will contribute air-deployed buoys to provide real time observations of hurricane waves and wave forcing that can be ingested by modeling groups, improving forecasts and validating hindcasts. |
14 Dec 2021
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Wave Glider Observations in the Southern Ocean A Wave Glider autonomous surface vehicle will conduct a summer-season experiment to investigate oceanshelf exchange on the West Antarctic Peninsula and frontal airsea interaction over both the continental shelf and open ocean. |
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4 Sep 2019
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Southern Ocean climate change is at the heart of the ocean's response to anthropogenic forcing. Variations in South Polar atmospheric circulation patterns, fluctuations in the strength and position of the Antarctic Circumpolar Current, and the intertwining intermediate deep water cells of the oceanic meridional overturning circulation have important impacts on the rate of ocean carbon sequestration, biological productivity, and the transport of heat to the melting continental ice shelves. |
Wave Measurements at Ocean Weather Station PAPA As part of a larger project to understand the impact of surface waves on the ocean mixed layer, APL-UW is measuring waves at Ocean Weather Station Papa, a long-term observational site at N 50°, W 145°. |
29 Aug 2019
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Coastal Ocean Dynamics in the Arctic CODA Arctic coastlines are eroding at rates of meters per year. As the whole Arctic shifts into a modern epoch of seasonal ice cover and warmer temperatures, Arctic coastal processes are shifting, too. The overall goal of this research is to improve scientific understanding of waveiceocean interactions along the Arctic coast, with particular attention to the oceanographic parameters that affect erosion. |
8 Jan 2019
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Stratified Ocean Dynamics of the Arctic SODA Vertical and lateral water properties and density structure with the Arctic Ocean are intimately related to the ocean circulation, and have profound consequences for sea ice growth and retreat as well as for prpagation of acoustic energy at all scales. Our current understanding of the dynamics governing arctic upper ocean stratification and circulation derives largely from a period when extensive ice cover modulated the oceanic response to atmospheric forcing. Recently, however, there has been significant arctic warming, accompanied by changes in the extent, thickness distribution, and properties of the arctic sea ice cover. The need to understand these changes and their impact on arctic stratification and circulation, sea ice evolution, and the acoustic environment motivate this initiative. |
31 Oct 2016
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Inner Shelf Dynamics The inner shelf region begins just offshore of the surf zone, where breaking by surface gravity waves dominate, and extends inshore of the mid-shelf, where theoretical Ekman transport is fully realized. Our main goal is to provide provide improved understanding and prediction of this difficult environment. This will involve efforts to assess the influence of the different boundaries surf zone, mid and outer shelf, air-water interface, and bed on the flow, mixing and stratification of the inner shelf. We will also gain information and predictive understanding of remotely sensed surface processes and their connection to processes in the underlying water column. |
15 Dec 2015
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Measuring Vessel Wakes in Rich Passage, Puget Sound APL-UW is using wave buoys to measure the wakes of Washington State DOT car ferries as they transit through Rich Passage. The objective is to assess the effectiveness of the speed reduction protocol through the passage, which is intended to minimize the vessel wake and minimize any subsequent changes to the shoreline. |
22 Oct 2014
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Tidal Flats Under an ONR-sponsored Department Research Initiative researchers are studying thermal signatures of inter-tidal sediments. The goal is to understand how sediment properties feedback on morphology and circulation, and the extent to which such properties |
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Wave Dissipation and the Distribution of Breaking Crests The energy dissipation of breaking waves is quantified using simultaneous remote and in situ measurements. |
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Northwest National Marine Renewable Energy Center Researchers at the University of Washington and Oregon State University are developing mobile instrumentation and methods for cost-effective environmental and performance monitoring of tidal in-stream energy conversion devices. |
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Videos
microSWIFTs: Tiny Oceanographic Floats Measure Extreme Coastal Conditions These small, inexpensive ocean drifters are the latest generation of the Surface Wave Instrument Float with Tracking (SWIFT) platform developed at APL-UW. They are being used in several collaborative research experiments to increase the density of nearshore wave observations. |
19 Apr 2022
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Using a Wave Energy Converter for UUV Recharge This project demonstrates the interface required to operate, dock, and wirelessly charge an uncrewed underwater vehicle with a wave energy converter. |
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11 Apr 2022
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Uncrewed underwater vehicles (UUVs) predominantly use onboard batteries for energy, limiting mission duration based on the amount of stored energy that can be carried by the vehicle. Vehicle recharge requires recovery using costly, human-supported vessel operations. The ocean is full of untapped energy in the form of waves that, when converted to electrical energy by a wave energy converter (WEC), can be used locally to recharge UUVs without human intervention. In this project we designed and developed a coupled WEC-UUV system, with emphasis on the systems developed to interface the UUV to the WEC. |
Mapping Underwater Turbulence with Sound |
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9 Apr 2018
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To dock at a terminal, large Washington State ferries use their powerful engines to brake, generating a lot of turbulence. Doppler sonar instruments are capturing an accurate picture of the turbulence field during docking procedures and how it affects terminal structures and the seabed. This research is a collaborative effort between APL-UW and the UW College of Engineering, Department of Civil and Environmental Engineering. |
Marine Renewable Energy: Kvichak River Project At a renewable energy site in the village of Igiugig, Alaska, an APL-UW and UW Mechanical Engineering team measured the flow around an electricity-generating turbine installed in the Kvichak River. They used modified SWIFT buoys and new technologies to measure the natural river turbulence as well as that produced by the turbine itself. The turbine has the capacity to generate a sizable share of the village's power needs. |
25 Sep 2014
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Ferry-Based Monitoring of Puget Sound Currents Acoustic Doppler Current Profilers are installed on two Washington State Department of Transportation ferries to measure current velocities in a continuous transect along their routes. WSDOT ferries occupy strategic cross-sections where circulation and exchange of Puget Sound and Pacific Ocean waters occurs. A long and continuous time series will provide unprecedented measurements of water mass movement and transport between the basins. |
9 May 2014
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DARLA: Data Assimilation and Remote Sensing for Littoral Applications Investigators completed a series of experiments in April 2013 at the mouth of the Columbia River, where they collected data using drifting and airborne platforms. DARLA's remote sensing data will be used to drive representations of the wave, circulation, and bathymetry fields in complex near-shore environments. |
5 Dec 2013
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Marginal Ice Zone (MIZ) Program An integrated program of observations and numerical simulations will focus on understanding iceoceanatmosphere dynamics in and around the MIZ, with particular emphasis on quantifying changes associated with decreasing ice cover. The MIZ measurement program will employ a novel mix of autonomous technologies (ice-based instrumentation, floats, drifters, and gliders) to characterize the processes that govern Beaufort Sea MIZ evolution from initial breakup and MIZ formation though the course of the summertime sea ice retreat. |
22 Mar 2013
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Turbulence Generated by Tides in the Canal de Chacao, Chile At a proposed tidal energy conversion site in southern Chile, APL-UW researchers are measuring the magnitude and scales of turbulence, both to aid in the design of turbines for the site and to understand the fundamental dynamics of flows through the channel. |
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7 Mar 2013
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Principal Investigator Jim Thomson chronicled all phases of the Chilean experiment through posts to the New York Times 'Scientist at Work' blog. |
Sea State and Boundary Layer Physics of the Emerging Arctic Ocean This ONR Departmental Research Initiative is in response to the observed decline in Arctic sea ice extent. The U.S. Navy has a renewed interest in understanding and predicting the environment in this region, including a desire to forecast the presence or absence of sea ice at a variety of lead times. |
7 Mar 2013
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Storm Chasing in the North Pacific A research cruise was conducted in October 2012 to find stormy conditions and heavy seas far out in the Pacific Ocean. The objectives were to measure, with remote sensing technologies, the intense winds, large waves, and the turbulence generated by wave breaking. Understanding the balance of energy going into and breaking out of waves will be used to improve open ocean wave forecasts. |
2 Nov 2012
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Sound Sounds: Listening to the Undersea Noise in Puget Sound Doctoral student researcher Chris Bassett is analyzing a long time series of ambient noise data from Puget Sound. Vessel traffic is the most significant noise source, but breaking waves, precipitation, biology, and sediment moving on the seabed are other common underwater noise sources. The research is being pursued in conjunction with a program to assess the environmental impacts from a tidal energy conversion system placed on the seafloor. |
13 Mar 2012
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SWIFT: Surface Wave Instrument Float with Tracking The Surface Wave Instrumentation Float with Tracking is a free drifting system to measure turbulence and noise at the ocean surface. |
23 Jan 2012
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Wave Breaking in Mixed Seas Waves are generated by wind blowing across the ocean and dissipated by breaking, either as whitecaps or surf. This research aims to understand the breaking process and the resulting turbulence, especially in wave fields that are a mix of wind waves and swell. Measurements from APL-UW SWIFT instruments quantify the turbulence and the wave motions. Additional video measurements quantify the size distribution of the breakers. Applications include improved wave forecasting and parameterization of gas exchange. |
12 Apr 2011
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Tidal Power from the Seafloor Researchers are conducting an extensive survey of the oceanographic properties of a proposed tidal energy site in Puget Sound to inform the safety and effectiveness of power-generating turbines. |
1 Nov 2010
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Publications |
2000-present and while at APL-UW |
The 2019 marine heatwave at Ocean Station Papa: A multi-disciplinary assessment of ocean conditions and impacts on marine ecosystems Kohlman, C., and 9 others including J. Thomson, "The 2019 marine heatwave at Ocean Station Papa: A multi-disciplinary assessment of ocean conditions and impacts on marine ecosystems," J. Geophys. Res., 129, doi:10.1029/2023JC020167, 2024. |
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21 Jun 2024 |
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In the past decade, two large marine heatwaves (MHWs) formed in the northeast Pacific near Ocean Station Papa (OSP), one of the oldest oceanic time series stations. Physical, biogeochemical, and biological parameters observed at OSP from 2013 to 2020 are used to assess ocean response and potential impacts on marine life from the 2019 northeast Pacific MHW. The 2019 MHW reached peak surface and subsurface temperature anomalies in the summertime and had both coastal, impacting fisheries, and offshore consequences that could potentially affect multiple trophic levels in the Gulf of Alaska. In the Gulf of Alaska, the 2019 MHW was preceded by calm and stratified upper ocean conditions, which preconditioned the enhanced surface warming in late spring and early summer. The MHW coincided with lower dissolved inorganic carbon and higher pH of surface waters relative to the 20132020 period. A spike in the summertime chlorophyll followed by a decrease in surface macronutrients suggests increased productivity in the well-lit stratified upper ocean during summer 2019. More blue whale calls were recorded at OSP in 2019 compared to the prior year. This study shows how the utility of long-term, continuous oceanographic data sets and analysis with an interdisciplinary lens is necessary to understand the potential impact of MHWs on marine ecosystems. |
Statistics of bubble plumes generated by breaking surface waves Derakhti, M., J. Thomson, C. Bassett, M. Malila, and J.T. Kirby, "Statistics of bubble plumes generated by breaking surface waves," J. Geophys. Res., 129, doi:10.1029/2023JC019753, 2024. |
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17 May 2024 |
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We examine the dependence of the penetration depth and fractional surface area (e.g., whitecap coverage) of bubble plumes generated by breaking surface waves on various wind and wave parameters over a wide range of sea state conditions in the North Pacific Ocean, including storms with sustained winds up to 22 m s-1 and significant wave heights up to 10 m. Our observations include arrays of freely drifting SWIFT buoys together with shipboard systems, which enabled concurrent high-resolution measurements of wind, waves, bubble plumes, and turbulence. We estimate bubble plume penetration depth from echograms extending to depths of more than 30 m in a surface-following reference frame collected by downward-looking echosounders integrated onboard the buoys. Our observations indicate that mean and maximum bubble plume penetration depths exceed 10 and 30 m beneath the surface during high winds, respectively, with plume residence times of many wave periods. They also establish strong correlations between bubble plume depths and wind speeds, spectral wave steepness, and whitecap coverage. Interestingly, we observe a robust linear correlation between plume depths, when scaled by the total significant wave height, and the inverse of wave age. However, scaled plume depths exhibit non-monotonic variations with increasing wind speeds. Additionally, we explore the dependencies of the combined observations on various non-dimensional predictors used for whitecap coverage estimation. This study provides the first field evidence of a direct relation between bubble plume penetration depth and whitecap coverage, suggesting that the volume of bubble plumes could be estimated by remote sensing. |
Measuring turbulence from wave-following platforms Zeiden, K., and J. Thomson, "Measuring turbulence from wave-following platforms," In Proc., IEEE/OES 13th Current, Waves and Turbulence Measurement (CWTM), 18-20 March 2024, Wanchese, NC, doi:10.1109/CWTM61020.2024.10526345 (IEEE, 2024). |
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15 May 2024 |
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Autonomous surface platforms equipped with pulse-coherent high-resolution (HR) ADCPs are a promising tool for measuring turbulence and estimating turbulent dissipation rates, ε(z), close to the air-sea interface. However, surface gravity waves generate significant bias in ε(z) if not sufficiently separated from the turbulent signal. In a previous study, the authors developed a method of isolating wave orbital velocities from the data using empirical orthogonal functions (EOFs). Low-mode EOFs had characteristics of surface gravity waves, while higher-mode EOFs had characteristics of turbulence. After filtering empirical wave profiles constructed from the low-mode EOFs from the data, resultant ε(z) were in close agreement with law-of-the-wall scaling during quiescent conditions. In this study, we further validate the EOF-filtering technique by comparing EOFs of the HR ADCP data with those computed from synthetic wave data which does not contain turbulence. As expected, low-mode EOFs of the synthetic data are in strong agreement with those of the real data, while high-mode EOFs reflect only noise due to the absence of turbulence. Wave profiles constructed from the low-mode EOFs are then used to quantify the potential for bias in ε(z) if wave velocities are not sufficiently filtered from the data. |
Multiscale measurements of hurricane waves using buoys and airborne radar Davis, J.R., J. Thomson, B.J. Butterworth, I.A. Houghton, C. Fairall, E.J. Thompson, and G. de Boer, "Multiscale measurements of hurricane waves using buoys and airborne radar," In Proc., IEEE/OES 13th Current, Waves and Turbulence Measurement (CWTM), 18-20 March 2024, Wanchese, NC, doi:10.1109/CWTM61020.2024.10526332 (IEEE, 2024). |
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15 May 2024 |
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The processes important to hurricane wave generation cover scales from kilometers to centimeters. Within a storm, waves have complex spatial variations that are sensitive to hurricane size, strength and speed. This makes it challenging to measure the spatial variability of hurricane waves with any single instrument. To obtain both broad spatial coverage and resolve the full range of wave scales, we combine arrays of drifting wave buoys with airborne radar altimetry. The microSWIFT (UW-APL) and Spotter (Sofar) buoys are air-deployed along a given storm track. These buoys resolve the scalar wave frequency spectrum from 0.05 Hz to 0.5 Hz, which is approximately 600 m to 6 m wavelength (in deep water). The Wide Swath Radar Altimeter (WSRA) flies into hurricanes aboard the NOAA Hurricane Hunter P-3 aircraft. The radar altimetry data is processed to produce a 2D directional spectrum from 2.5 km to 80 m wavelength, and the radar backscatter provides an estimate of the mean square slope down to centimeter wavelengths. We introduce a method to use colocated mean square slope observations from each instrument to infer the shape of the spectral tail from 0.5 Hz to almost 3 Hz. The method is able to recover the frequency f5 tail characteristic of the saturation range expected at these frequencies (based on theory and measurements in lower wind speeds). We also explore the differences between WSRA and buoy mean square slopes, which represent the mean square slope of the intermediate wavelength waves (6 m down to 20 cm). Together, the fusion of these wave measurements provides a multiscale view of the hurricane-generated waves. These ocean surface waves are critical as drivers of the air-sea coupling that controls storm evolution and as drivers of coastal impacts by hurricanes. |
The next wave: Buoy arrays for deterministic wave prediction in real-time Thomson, J., A. Fisher, and C.J. Rusch, "The next wave: Buoy arrays for deterministic wave prediction in real-time," In Proc., IEEE/OES 13th Current, Waves and Turbulence Measurement (CWTM), 18-20 March 2024, Wanchese, NC, doi:10.1109/CWTM61020.2024.10526333 (IEEE, 2024). |
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15 May 2024 |
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This work uses sparse arrays of ocean wave buoys to create a linear reconstruction of the sea surface and provide deterministic wave predictions at a future time and nearby position (i.e., within a few wavelengths). The predictions are constrained to be within the statistics of recently observed waves. This recently established method is applied in post-processing at two distinct projects related to 1) a wave energy converter and 2) an offshore wind platform. The conditions range from scale-model tank testing to an operational open-ocean wind farm. Relative to a conventional statistical forecasting with random waves, the method achieves at least 60% improvement in prescribing the next several waves arriving at a given target location. Work is ongoing to implement this method in realtime, using radio modems to transmit raw motion data (5 Hz sampling) from the buoy array to a central node that continually updates a 30-second prediction window with less than 1-second latency. The deterministic wave predictions can be used to improve control strategies for platforms at sea, with improvements in efficiency and reductions in dynamic loads. |
Morphology and sediment dynamics of blossom shoals at Icy Cape, Alaska Eidam, E.F., J. Thomson, J.G. Malito, and L. Hošeková, "Morphology and sediment dynamics of blossom shoals at Icy Cape, Alaska," J. Geophys. Res., 129, doi:10.1029/2023JF007398, 2024. |
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1 Apr 2024 |
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Capes and cape-associated shoals represent sites of convergent sediment transport, and can provide points of relative coastal stability, navigation hazards, and offshore sand resources. Shoal evolution is commonly impacted by the regional wave climate. In the Arctic, changing sea-ice conditions are leading to (a) longer open-water seasons when waves can contribute to sediment transport, and (b) an intensified wave climate (related to duration of open water and expanding fetch). At Blossom Shoals offshore of Icy Cape in the Chukchi Sea, these changes have led to a five-fold increase in the amount of time that sand is mobile at a 31-m water depth site between the period 19531989 and the period 19902022. Wave conditions conducive to sand transport are still limited to less than 2% of the year, however, and thus it is not surprising that the overall morphology of the shoals has changed little in 70 years, despite evidence of active sand transport in the form of 1-m-scale sand waves on the flanks of the shoals, which heal ice keel scours formed during the winter. Suspended-sediment transport is relatively weak due to limited sources of mud nearby, but can be observed in a net northeastward direction during the winter (driven by the Alaska Coastal Current under the ice) and in a southwestward direction during open-water wind events. Longer open-water seasons mean that annual net northeastward transport of fine sediment may weaken, with implications for the residence time of fine-grained sediments and particle-associated nutrients in the Chukchi Sea. |
Performance of moored GPS wave buoys Collins, C.O., and 10 others including J. Thomson, "Performance of moored GPS wave buoys," Coast. Eng. J., EOR, doi:10.1080/21664250.2023.2295105, 2024. |
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30 Jan 2024 |
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Small, lightweight, and easy-to-deploy Global Positioning Satellite (GPS)-based miniature wave buoys (mini-buoys) are increasing in popularity. Most are deployed as Lagrangian drifters, so their utility for engineering applications, requiring a nearshore mooring, has remained in question. We evaluated the performance of five moored mini-buoys off the coast of Duck, North Carolina at Field Research Facility (FRF). We collected 8 months of data over two deployments; first near the FRF’s 8-m array and then near a Datawell Waverider in 17-m depth. We deployed an Acoustic Doppler Current Profiler (ADCP) that measured waves and currents, and compared it to the nearby operational system as a performance benchmark for the mini-buoys. The mini-buoys performed well, with statistics similar to the benchmark for wave frequency spectra and spectral parameters, and they outperformed the benchmark on directional parameters. However, mini-buoy communication was sometimes interrupted by tilting or submersion, which manifested as low-frequency noise or drop-outs. If a mooring was taut, forced by winds or currents and exacerbated by tangled lines or shallower depths, then mini-buoys were more susceptible to communication issues. Overall, these issues were rare; thus, mini-buoys were found to be appropriate for many applications. |
Measurements of nearshore ocean-surface kinematics through coherent arrays of free-drifting buoys Rainville, E., J. Thomson, M. Moulton, and M. Derakhti, "Measurements of nearshore ocean-surface kinematics through coherent arrays of free-drifting buoys," Earth Syst. Sci. Data, 15, 5135-5151, doi:10.5194/essd-15-5135-2023, 2023. |
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27 Nov 2023 |
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Surface gravity wave breaking occurs along coastlines in complex spatial and temporal patterns that significantly impact erosion, scalar transport, and flooding. Numerical models are used to predict wave breaking and associated processes but many lack sufficient evaluation with observations. To fill the need for more nearshore wave measurements, we deployed coherent arrays of small-scale, free-drifting buoys named microSWIFTs. The microSWIFT is a small buoy equipped with a GPS module to measure the buoy's position, horizontal velocities, and an inertial measurement unit (IMU) to directly measure the buoy's rotation rates, accelerations, and heading. Measurements were collected over a 27 d field experiment in October 2021 at the US Army Corps of Engineers Field Research Facility in Duck, NC. The microSWIFTs were deployed as a series of coherent arrays, meaning they all sampled simultaneously with a common time reference, leading to a rich spatial and temporal dataset during each deployment. Measurements spanned offshore significant wave heights ranging from 0.5 to 3 m and peak wave periods ranging from 5 to 15 s over the entire experiment. |
Development and testing of microSWIFT expendable wave buoys Thomson, J., P. Bush, V.C. Contreras, N. Clemett, J. Davis, A. de Klerk, E. Iseley, E.J. Rainville, B. Salmi, and J. Talbert, "Development and testing of microSWIFT expendable wave buoys," Coastal Eng. J., EOR, doi:10.1080/21664250.2023.2283325, 2023. |
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22 Nov 2023 |
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Expendable microSWIFT buoys have been developed and tested for measuring ocean surface waves. Wave spectra are calculated via onboard processing of GPS velocities sampled at 5 Hz, and wave spectra are delivered to a shore-side server via Iridium modem once per hour. The microSWIFTs support additional sensor payloads, in particular seawater conductivity and temperature. The buoys have a non-traditional, cylindrical shape that is required for deployment via the dropsonde tube of research aircraft. Multiple versions have been developed and tested, with design considerations that include: buoy hydrodynamics, sensor noise, algorithm tuning, processor power, and ease of deployment. Field testing in a range of conditions, including near sea ice and in a hurricane, has validated the design. |
Acoustic backscattering at a tidal intrusion front Bassett, C., and 9 others including J. Thomson, "Acoustic backscattering at a tidal intrusion front," Prog. Oceanogr., EOR, doi:10.1016/j.pocean.2023.103167, 2023. |
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8 Nov 2023 |
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Strong spatial gradients and rapidly evolving, three-dimensional structure make estuarine fronts difficult to sample. Echosounders can be used near fronts to provide nearly synoptic images of water column processes and, with sufficient bandwidth, can provide quantitative information about dynamical variables derived from forward and inverse methods using acoustic backscattering measurements. This manuscript discusses measurements using broadband (50-420 kHz) echosounders from the James River (Virginia, USA) tidal intrusion front. The dominant backscattering mechanisms observed at the site include bubbles, turbulent microstructure, interfaces associated with stratification, suspended sediment, and biota. Existing analytical models are used to interpret contributions from these sources with acoustic inversions providing quantitative information about the physical structure and processes that compare favorably with conventional, in situ measurements. Supporting data sets for this analysis include measurements of temperature, salinity, velocity, and turbidity; X-band radar images of sea surface roughness; aerial optical imagery; Lagrangian measurements of waves, turbulence, and velocity structure; and Regional Ocean Modeling System circulation model simulations. A notable advantage of acoustic remote sensing is the ability to resolve processes at considerably higher spatial resolution (< 1 m horizontal; < 5 cm vertical) than other in situ sampling approaches. |
Investigating Storm Resilience of United States Coast Guard Fixed Aids to Navigation Structures McClintic, B., J. Thomson, R. Luettich, and J. Spilsbury, "Investigating Storm Resilience of United States Coast Guard Fixed Aids to Navigation Structures," Technical Report, APL-UW TR 2306, Applied Physics Laboratory, University of Washington, Seattle, November 2023, 24 pp. |
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7 Nov 2023 |
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Hurricanes along the United States Gulf and East coasts are becoming more intense, slower moving, and costlier than ever as the world’s climate warms. The United States Coast Guard (USCG), which operates and maintains the nation's Aids to Navigation (ATON) system, is experiencing increasing ATON infrastructure damage after each storm. This project investigates how the USCG can apply modeled hurricane data to best understand the environmental conditions that various ATON structure types are most vulnerable to in a storm. The project uses Hurricane Ian in 2022 as a case study and focuses on structures consisting of a single pile. The distributions of maximum wind speed, wave height, and water elevation experienced at locations of aids that failed during the storm were compared to the distributions of the same parameters at aids that did not experience any issues. The study found that discrepant single-pile ATON had a higher probability of having experienced high wind speed and wave height during Hurricane Ian than non-discrepant ATON, while no difference was observed between the distribution of water elevation at discrepant versus non-discrepant ATON. Thus, high wind speeds and wave heights are likely drivers of damage to single-pile ATON during major storms, but higher water level is not. More importantly, these results show that modeled hurricane data is useful to reveal vulnerabilities in USCG infrastructure. If the USCG applies these methods to analyze different structure types, categories of storms, and discrepancy types (e.g., structural failure, missing dayboard, extinguished light, etc.), the resulting conclusions may reveal probabilistic trends of discrepancies that will aid both short-term equipment preparation and long-term strategic and financial planning ahead of a hurricane season, improving the service's resiliency towards future storms. |
PMEL ocean climate stations as reference time series and research aggregate devices Cronin, M.F., and 14 others including J. Yang and J. Thomson, "PMEL ocean climate stations as reference time series and research aggregate devices," Oceanography, 36, 46-53, doi:10.5670/oceanog.2023.224, 2023. |
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30 Oct 2023 |
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The NOAA Pacific Marine Environmental Laboratory (PMEL) Ocean Climate Stations (OCS) project provides in situ measurements for quantifying air-sea interactions that couple the ocean and atmosphere. The project maintains two OceanSITES surface moorings in the North Pacific, one at the Kuroshio Extension Observatory in the Northwest Pacific subtropical recirculation gyre and the other at Station Papa in the Northeast Pacific subpolar gyre. OCS mooring time series are used as in situ references for assessing satellite and numerical weather prediction models. A spinoff of the PMEL Tropical Atmosphere Ocean (TAO) project, OCS moorings have acted as "research aggregating devices." Working with and attracting wide-ranging partners, OCS scientists have collected process-oriented observations of variability on diurnal, synoptic, seasonal, and interannual timescales, and trends associated with anthropogenic climate change. Since 2016, they have worked to expand, test, and verify the observing capabilities of uncrewed surface vehicles and to develop observing strategies for integrating these unique, wind-powered observing platforms within the tropical Pacific and global ocean observing system. PMEL OCS has been at the center of the UN Decade of Ocean Sciences for Sustainable Development (20212030) effort to develop an Observing Air-Sea Interactions Strategy (OASIS) that links an expanded network of in situ air-sea interaction observations to optimized satellite observations, improved ocean and atmospheric coupling in Earth system models, and ultimately improved ocean information across an array of essential climate variables for decision-makers. This retrospective highlights not only achievements of the PMEL OCS project but also some of its challenges. |
Observations of ocean surface wave attenuation in sea ice using seafloor cables Smith, M.M., J. Thomson, M.G. Baker, R.E. Abbott, and J. Davis, "Observations of ocean surface wave attenuation in sea ice using seafloor cables," Geophys. Res. Lett., 50, doi:10.1029/2023GL105243, 2023. |
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28 Oct 2023 |
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The attenuation of ocean surface waves during seasonal ice cover is an important control on the evolution of Arctic coastlines. The spatial and temporal variations in this process have been challenging to resolve with conventional sampling using sparse arrays of moorings or buoys. We demonstrate a novel method for persistent observation of wave-ice interactions using distributed acoustic sensing (DAS) along existing seafloor fiber optic telecommunications cables. DAS measurements span a 36-km cross-shore cable on the Beaufort Shelf from Oliktok Point, Alaska. DAS optical sensing of fiber strain-rate provides a proxy for seafloor pressure, which we calibrate with wave buoy measurements during the ice-free season (August 2022). We apply this calibration during the ice formation season (November 2021) to obtain unprecedented resolution of variable wave attenuation rates in new, partial ice cover. The location and strength of wave attenuation serve as proxies for ice coverage and thickness, especially during rapidly evolving events. |
Estimating profiles of dissipation rate in the upper ocean using acoustic Doppler measurements made from surface following platforms Zeiden, K., J. Thomson, and J. Girton, "Estimating profiles of dissipation rate in the upper ocean using acoustic Doppler measurements made from surface following platforms," J. Atmospheric. Ocean. Technol., 40, 1383-1401, doi:10.1175/JTECH-D-23-0027.1, 2023. |
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13 Oct 2023 |
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High resolution profiles of vertical velocity obtained from two different surface-following autonomous platforms, Surface Wave Instrument Floats with Tracking (SWIFTs) and a Liquid Robotics SV3 Wave Glider, are used to compute dissipation rate profiles ε (z) between 0.5 and 5 m depth via the structure function method. The main contribution of this work is to update previous SWIFT methods (Thomson 2012) to account for bias due to surface gravity waves, which are ubiquitous in the near-surface region. We present a technique where the data are pre-filtered by removing profiles of wave orbital velocities obtained via empirical orthogonal function (EOF) analysis of the data prior to computing the structure function. Our analysis builds on previous work to remove wave bias in which analytic modifications are made to the structure function model (Scannell et al. 2017). However, we find the analytic approach less able to resolve the strong vertical gradients in ε (z) near the surface. The strength of the EOF filtering technique is that it does not require any assumptions about the structure of non-turbulent shear, and does not add any additional degrees of freedom in the least-squares fit to the model of the structure function. In comparison to the analytic method, ε (z) estimates obtained via empirical filtering have substantially reduced noise and clearer dependence on near-surface wind speed. |
Direct observations of wavesea ice interactions in the Antarctic marginal ice zone Wahlgren, S., J. Thomson, L.C. Biddle, and S. Swart, "Direct observations of wavesea ice interactions in the Antarctic marginal ice zone," J. Geophys. Res., 128, doi:10.1029/2023JC019948, 2023. |
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1 Oct 2023 |
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Wave energy propagating into the Antarctic marginal ice zone effects the quality and extent of the sea ice, and wave propagation is therefore an important factor for understanding and predicting changes in sea ice cover. Wavesea ice interactions are notoriously hard to model and in-situ observations of wave activity in the Antarctic marginal ice zone are scarce, due to the extreme conditions of the region. Here, we provide new in-situ data from two drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys deployed in the Weddell Sea in the austral winter and spring of 2019. The buoy location ranges from open water to more than 200 km into the sea ice. We estimate the attenuation of swell with wave periods 818 s, and find an attenuation coefficient α = 4 x 10-6 to 7 x 10-5 m-1 in spring, and approximately five-fold larger in winter. The attenuation coefficients show a power law frequency dependence, with power coefficient close to literature. The in-situ data also shows a change in wave direction, where wave direction tends to be more perpendicular to the ice edge in sea ice compared to open water. A possible explanation for this might be a change in the dispersion relation caused by sea ice. These observations can help shed further light on the influence of sea ice on waves propagating into marginal ice zones, aiding development of coupled wavesea ice models. |
Direct observations of wavesea ice interactions in the Antarctic marginal ice zone Wahlgren, S., J. Thomson, L.C. Biddle, and S. Swart, "Direct observations of wavesea ice interactions in the Antarctic marginal ice zone," J. Geophys. Res., 128, doi:10.1029/2023JC019948, 2023. |
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1 Oct 2023 |
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Changes in the sea ice extent around Antarctica affects the global climate, and it is therefore important to accurately represent sea ice in climate models. One feature that is generally missing in climate models is the interaction between ocean waves and sea ice. Ocean waves change the sea ice, for example, by breaking up ice floes into smaller ones. At the same time, the sea ice reduces the strength of the waves so that the wave height decreases and eventually disappears far into the sea ice. How far into the sea ice waves reach depends both on the size of the waves and on the sea ice, and can be very different depending on for example, ice thickness, size of floes and age. In order to better represent the wavesea ice interactions in climate models, simple but accurate models of how fast sea ice reduces the strength of waves is needed. Using wave buoys, we measured the wave activity in the Antarctic sea ice during two expeditions in 2019. We found a notable difference between spring and winter, where the waves were reduced much faster in winter than in spring. This can help to improve predictions of sea ice cover. |
Saturation of ocean surface wave slopes observed during hurricanes Davis, J.R., J. Thomson, I.A. Houghton, J.D. Doyle, W.A. Komaromi, C.W. Fairall, E.J. Thompson, and J.R. Moskaitis, "Saturation of ocean surface wave slopes observed during hurricanes," Geophys. Res. Lett., 50, doi:10.1029/2023GL104139, 2023. |
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28 Aug 2023 |
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Drifting buoy observations of ocean surface waves in hurricanes are combined with modeled surface wind speeds. The observations include targeted aerial deployments into Hurricane Ian (2022) and opportunistic measurements from the Sofar Ocean Spotter global network in Hurricane Fiona (2022). Analysis focuses on the slope of the waves, as quantified by the spectral mean square slope. At low-to-moderate wind speeds (<15 ms-1), slopes increase linearly with wind speed. At higher winds (>15 ms-1), slopes continue to increase, but at a reduced rate. At extreme winds (>30 ms-1), slopes asymptote. The mean square slopes are directly related to the wave spectral shapes, which over the resolved frequency range (0.030.5 Hz) are characterized by an equilibrium tail (f-4) at moderate winds and a saturation tail (f-5) at higher winds. The asymptotic behavior of wave slope as a function of wind speed could contribute to the reduction of surface drag at high wind speeds. |
Wave Exposure on the Northern Coast of Alaska Using the SWAN Model with a Sea Ice Parameterization Hošeková, L., W.E. Rogers, and J. Thomson, "Wave Exposure on the Northern Coast of Alaska Using the SWAN Model with a Sea Ice Parameterization," Technical Report, APL-UW TR 2302, Applied Physics Laboratory, University of Washington, Seattle, May 2023, 24 pp. |
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8 May 2023 |
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The presence of sea ice along Arctic coastlines controls the exposure of the coast to wave action. We present a case study from the summer of 2014 to demonstrate the recent addition of ice attenuation in the SWAN (Simulating WAves Nearshore) numerical wave model. Observations from several freely drifting SWIFT (Surface Wave Instrument Float with Tracking) buoys show reduced wave action resulting from remnant sea ice along the coast in early summer. This is well-described by the new model that includes sea ice attenuation, relative to a previous version of the wave model without a sea ice parameterization. The model is sensitive to the sea ice product used for model initialization because some sea ice products do not resolve coastal ice. The difference in the cumulative wave exposure at the coast shows that sea ice attenuation in early summer is a significant seasonal effect. |
Wind-driven motions of the ocean surface mixed layer in the Western Arctic Brenner, S., J. Thomson, L. Rainville, L. Crews, and C. Lee, "Wind-driven motions of the ocean surface mixed layer in the Western Arctic," J. Phys. Oceanogr., 53, 1787-1804, doi:10.1175/JPO-D-22-0112.1, 2023. |
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12 Apr 2023 |
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Observations of sea ice and the upper ocean from three moorings in the Beaufort Sea quantify atmosphere-ice-ocean momentum transfer, with a particular focus on the inertial-frequency response. Seasonal variations in the strength of mixed layer (ML) inertial oscillations suggest that sea ice damps momentum transfer from the wind to the ocean, such that the oscillation strength is minimal under sea ice cover. In contrast, the net Ekman transport is unimpacted by the presence of sea ice. The mooring measurements are interpreted with a simplified one-dimensional ice-ocean coupled "slab" model. The model results provide insight into the drivers of the inertial seasonality: namely, that a combination of both sea ice internal stress and ocean ML depth contribute to the seasonal variability of inertial surface currents and inertial sea ice drift, while under-ice roughness does not. Furthermore, the importance of internal stress in damping inertial oscillations is different at each moorings, with a minimal influence at the southernmost mooring (within the seasonal ice zone) and more influence at the northernmost mooring. As the Arctic shifts to a more seasonal sea ice regime, changes in sea ice cover and sea ice internal strength may impact inertial-band ice-ocean coupling and allow for an increase in wind forcing to the ocean. |
Observations of river plume mixing in the surf zone Kastner, S.E., A.R. Horner-Devine, J.M. Thomson, and S.N. Giddings, "Observations of river plume mixing in the surf zone," J. Phys. Oceanogr., 53, doi:10.1175/JPO-D-21-0286.1, 2023. |
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1 Mar 2023 |
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We use salinity observations from drifters and moorings at the Quinault River mouth to investigate mixing and stratification in a surf-zone trapped river plume. We quantify mixing based on the rate of change of salinity, DS/Dt, in the drifters' quasi-Lagrangian reference frame. We estimate a constant value of the vertical eddy diffusivity of salt of Kz = 2.2±0.6×10-3 m2 s-1, based on the relationship between vertically integrated DS/Dt and stratification, with values as high as 1x10-2m2 s-1 when stratification is low. Mixing, quantified as DS/Dt, is directly correlated to surf-zone stratification, and is therefore modulated by changes in stratification caused by tidal variability in freshwater volume flux. High DS/Dt is observed when the near-surface stratification is high and salinity gradients are collocated with wave-breaking turbulence. We observe a transition from low stratification and low DS/Dt at low tidal stage to high stratification and high DS/Dt at high tidal stage. Observed wave-breaking turbulence does not change significantly with stratification, tidal stage or offshore wave height; as a result we observe no relationship between plume mixing and offshore wave height for the range of conditions sampled. Thus, plume mixing in the surf zone is altered by changes in stratification; these are due to tidal variability in freshwater flux from the river and not wave conditions, presumably because depth-limited wave breaking causes sufficient turbulence for mixing to occur during all observed conditions. |
Statistical and dynamical characteristics of extreme wave crests assessed with field measurements from the North Sea Malila, M.P., F. Barbariol, A. Benetazzo, Ø. Breivik, A.K. Magnusson, J. Thomson, and B. Ward, "Statistical and dynamical characteristics of extreme wave crests assessed with field measurements from the North Sea," J. Phys. Oceanogr., 53, doi:10.1175/JPO-D-22-0125.1, 2022. |
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1 Feb 2023 |
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Wave crests of unexpected height and steepness pose a danger to activities at sea, and long-term field measurements provide important clues for understanding the environmental conditions that are conducive to their generation and behavior. We present a novel data set of high-frequency laser altimeter measurements of the sea-surface elevation gathered over a period of 18 years from 2003 to 2020 on an offshore platform in the central North Sea. Our analysis of crest height distributions in the data set shows that mature, high sea states with high spectral steepness and narrow directional spreading exhibit crest height statistics that significantly deviate from standard second order models. Conversely, crest heights in developing sea states with similarly high steepness but wide directional spread correspond well to second order theory adjusted for broad frequency bandwidth. The long-term point time series measurements are complemented with space-time stereo video observations from the same location, collected during five separate storm events during the 20192020 winter season. An examination of the crest dynamics of the space-time extreme wave crests in the stereo video data set reveals that the crest speeds exhibit a slowdown localized around the moment of maximum crest elevation, in line with prevailing theory on nonlinear wave group dynamics. Extending on previously published observations focused on breaking crests, our results are consistent for both breaking and non-breaking extreme crests. We show that wave crest steepness estimated from time series using the linear dispersion relation may overestimate the geometrically measured crest steepness by up to 25% if the crest speed slowdown is not taken into account. |
Experimental validation of float array tidal current measurements in Agate Pass, WA Harrison, T.W., N. Clemett, B. Polagye, and J. Thomson, "Experimental validation of float array tidal current measurements in Agate Pass, WA," J. Atmos. Ocean. Technol., 40, 475-489, doi:10.1175/JTECH-D-22-0034.1, 2023. |
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12 Jan 2023 |
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Tidal currents, particularly in narrow channels, can be challenging to characterize due to high current speeds (> 1 m s-1), strong spatial gradients, and relatively short synoptic windows. To assess tidal currents in Agate Pass, WA, we cross-evaluated data products from an array of acoustically-tracked underwater floats and from acoustic Doppler current profilers (ADCPs) in both station-keeping and drifting modes. While increasingly used in basin-scale science, underwater floats have seen limited use in coastal environments. This study presents the first application of a float array towards small-scale (< 1 km), high resolution (< 5 m) measurements of mean currents in energetic tidal channel and utilizes a new prototype float, the μFloat, designed specifically for sampling in dynamic coastal waters. We show that a float array (20 floats) can provide data with similar quality to ADCPs, with measurements of horizontal velocity differing by less than 10% of nominal velocity, except during periods of low flow (0.1 m s-1). Additionally, floats provided measurements of the three dimensional temperature field, demonstrating their unique ability to simultaneously resolve in situ properties that cannot be remotely observed. |
Acoustic sensing of ocean mixed layer depth and temperature from uplooking ADCPs Brenner, S., J. Thomson, L. Rainville, D. Torres, M. Doble, J. Wilkinson, and C. Lee, "Acoustic sensing of ocean mixed layer depth and temperature from uplooking ADCPs," J. Atmos. Ocean. Technol., 40, doi:10.1175/JTECH-D-22-0055.1, 2022. |
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1 Jan 2023 |
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Properties of the surface mixed layer (ML) are critical for understanding and predicting atmosphere-sea ice-ocean interactions in the changing Arctic Ocean. Mooring measurements are typically unable to resolve the ML in the Arctic due to the need for instruments to remain below the surface to avoid contact with sea ice and icebergs. Here, we use measurements from a series of three moorings installed for one year in the Beaufort Sea to demonstrate that upward looking Acoustic Doppler Current Profilers (ADCPs) installed on subsurface floats can be used to estimate ML properties. A method is developed for combining measured peaks in acoustic backscatter and inertial shear from the ADCPs to estimate the ML depth. Additionally, we use an inverse sound speed model to infer the summer ML temperature based on offsets in ADCP altimeter distance during open water periods. The ADCP estimates of ML depth and ML temperature compare favourably with measurements made from mooring temperature sensors, satellite SST, and from an autonomous Seaglider. These methods could be applied to other extant mooring records to recover additional information about ML property changes and variability. |
Air-ice-ocean interactions and the delay of autumn freeze-up in the Western Arctic Ocean Thomson, J., M. Smith, K. Drushka, and C. Lee, "Air-ice-ocean interactions and the delay of autumn freeze-up in the Western Arctic Ocean," Oceanography, 35, 76-87, doi:10.5670/oceanog.2022.124, 2022. |
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1 Dec 2022 |
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Arctic sea ice is becoming a more seasonal phenomenon as a direct result of global warming. Across the Arctic, the refreezing of the ocean surface each autumn now occurs a full month later than it did just 40 years ago. In the western Arctic (Canada Basin), the delay is related to an increase in the seasonal heat stored in surface waters; cooling to the freezing point requires more heat loss to the atmosphere in autumn. In the marginal ice zone, the cooling and freezing process is mediated by ocean mixing and by the presence of remnant sea ice, which may precondition the ocean surface for refreezing. The delay in refreezing has many impacts, including increased open ocean exposure to autumn storms, additional wave energy incident to Arctic coasts, shifts in animal migration patterns, and extension of the time window for transit by commercial ships along the Northern Sea Route. This article reviews the observed trends in the western Arctic and the processes responsible for these trends, and provides brief in situ observations from the Beaufort Sea that illustrate some of these processes. |
Wave propagation in the marginal ice zone: Connections and feedback mechanisms within the airiceocean system Thomson, J., "Wave propagation in the marginal ice zone: Connections and feedback mechanisms within the airiceocean system," Phil. Trans. R. Soc. A., 380, doi:10.1098/rsta.2021.0251, 2022. |
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31 Oct 2022 |
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The propagation of ocean surface waves within the marginal ice zone (MIZ) is a defining phenomenon of this dynamic zone. Over decades of study, a variety of methods have been developed to observe and model wave propagation in the MIZ, with a common focus of determining the attenuation of waves with increasing distance into the MIZ. More recently, studies have begun to explore the consequences of wave attenuation and the coupled processes in the air–ice–ocean–land system. Understanding these coupled processes and effects is essential for accurate high-latitude forecasts. As waves attenuate, their momentum and energy are transferred to the sea ice and upper ocean. This may compact or expand the MIZ, depending on the conditions, while simultaneously modulating the wind work on the system. Wave attenuation is also a key process in coastal dynamics, where land–fast ice has historically protected both natural coasts and coastal infrastructure. With observed trends of increasing wave activity and retreating seasonal ice coverage, the propagation of waves within the MIZ is increasingly important to regional and global climate trends. |
Wind waves in sea ice of the western Arctic and a global coupled waveice model Cooper, V.T., L.A. Roach, J. Thomson, S.D. Brenner, M.M. Smith, M.H. Meylan, and C.M. Bitz, "Wind waves in sea ice of the western Arctic and a global coupled waveice model," Phil. Trans. R. Soc. A, 380, doi:10.1098/rsta.2021.0258, 2022. |
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31 Oct 2022 |
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The retreat of Arctic sea ice is enabling increased ocean wave activity at the sea ice edge, yet the interactions between surface waves and sea ice are not fully understood. Here, we examine in situ observations of wave spectra spanning 20122021 in the western Arctic marginal ice zone (MIZ). Swells exceeding 30 cm are rarely observed beyond 100 km inside the MIZ. However, local wind waves are observed in patches of open water amid partial ice cover during the summer. These local waves remain fetch-limited between ice floes with heights less than 1 m. To investigate these waves at climate scales, we conduct experiments varying wave attenuation and generation in ice with a global model including coupled interactions between waves and sea ice. A weak high-frequency attenuation rate is required to simulate the local waves in observations. The choices of attenuation scheme and wind input in ice have a remarkable impact on the extent of wave activity across ice-covered oceans, particularly in the Antarctic. As well as demonstrating the need for stronger constraints on wave attenuation, our results suggest that further attention should be directed towards locally generated wind waves and their role in sea ice evolution. |
Small-scale spatial variations of air-sea heat, moisture, and buoyancy fluxes in the tropical trade winds Iyer, S., K. Drushka, E.J. Thompson, and J. Thomson, "Small-scale spatial variations of air-sea heat, moisture, and buoyancy fluxes in the tropical trade winds," J. Geophys. Res., 127, doi:10.1029/2022JC018972, 2022. |
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1 Oct 2022 |
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Observations from two autonomous Wave Gliders and six Lagrangian Surface Wave Instrument Float with Tracking drifters in the northwestern tropical Atlantic during the JanuaryFebruary 2020 NOAA Atlantic Tradewind Ocean-atmosphere Mesoscale Interaction Campaign (ATOMIC) are used to evaluate the spatial variability of bulk air-sea heat, moisture, and buoyancy fluxes. Sea surface temperature (SST) gradients up to 0.7°C across 10100 km frequently persisted for several days. SST gradients were a leading cause of systematic spatial air-sea sensible heat flux gradients, as variations over 5 Wm-2 across under 20 km were observed. Wind speed gradients played no significant role and air temperature adjustments to SST gradients sometimes acted to reduce spatial flux gradients. Wind speed, air temperature, and air humidity caused high-frequency spatial and temporal flux variations on both sides of SST gradients. A synthesis of observations demonstrated that fluxes were usually enhanced on the warm SST side of gradients compared to the cold SST side, with variations up to 10 Wm-2 in sensible heat and upward buoyancy fluxes and 50 Wm-2 in latent heat flux. Persistent SST gradients and high-frequency air temperature variations each contributed up to 5 Wm-2 variability in sensible heat flux. Latent heat flux was instead mostly driven by air humidity variability. Atmospheric gradients may result from convective structures or high-frequency turbulent fluctuations. Comparisons with 0.05°-resolution daily satellite SST observations demonstrate that remote sensing observations or lower-resolution models may not capture the small-scale spatial ocean variability present in the Atlantic trade wind region. |
Relative current effect on short wave growth Guimarães, P.V., F. Ardhuin, Y. Perignon, A. Benetazzo, M.-N. Bouin, V. Garnier, J.-L. Redelsperger, M. Accensi, and J. Thomson, "Relative current effect on short wave growth," Ocean Dyn., 72, 621-639, doi:10.1007/s10236-022-01520-0, 2022. |
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6 Aug 2022 |
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Short waves growth is characterized by nonlinear and dynamic processes that couple ocean and atmosphere. Ocean surface currents can have a strong impact on short wave steepness and breaking, modifying the surface roughness, and consequently their growth. However, this interplay is poorly understood and observations are scarce. This work uses in situ measurements of near-surface winds, surface current, and waves under strong tidal current conditions to investigate the relative wind speed effect on the local short waves growth. Those observations were extensive compared with numerical modeling using WAVEWACHIII, where the simulations repeatedly fail to reproduce the observed wind sea energy under strong current conditions. Our field observations and coupled ocean-atmosphere numerical simulations suggest that surface currents can strongly modulate surface winds. That is a local process, better observed closer to the boundary layer than at 10 m height. Yet, it can cause a significant impact on the local wind shear estimation and consequently on the local waves’ growth source term. The results presented here show that the relative wind effect is not well solved inside spectral waves models, causing a significant bias around the peak of wind sea energy. |
Variations in wave slope and momentum flux from wavecurrent interactions in the tropical trade winds Iyer, S., J. Thomson, E. Thompson, and K. Drushka, "Variations in wave slope and momentum flux from wavecurrent interactions in the tropical trade winds," J. Geophys. Res., 127, doi:10.1029/2021JC018003, 2022. |
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1 Mar 2022 |
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Observations from six Lagrangian Surface Wave Instrument Float with Tracking drifters in JanuaryFebruary 2020 in the northwestern tropical Atlantic during the Atlantic Tradewind Oceanatmosphere Mesoscale Interaction Campaign are used to evaluate the influence of wavecurrent interactions on wave slope and momentum flux. At observed wind speeds of 4–12 ms-1, wave mean square slopes are positively correlated with wind speed. Wave-relative surface currents varied significantly, from opposing the wave direction at 0.24 ms-1 to following the waves at 0.47 ms-1. Wave slopes are 5%10% higher when surface currents oppose the waves compared to when currents strongly follow the waves, consistent with a conservation of wave energy flux across gradients in currents. Assuming an equilibrium frequency range in the wave spectrum, wave slope is proportional to wind friction velocity and momentum flux. The observed variation in wave slope equates to a 10%20% variation in momentum flux over the range of observed wind speeds (412 ms-1), with larger variations at higher winds. At wind speeds over 8 ms-1, momentum flux varies by at least 6% more than the variation expected from current-relative winds alone, and suggests that wave-current interactions can generate significant spatial and temporal variability in momentum fluxes in this region of prevailing trade winds. Results and data from this study motivate the continued development of fully coupled atmosphere-ocean-wave models. |
Direct observations of the role of lateral advection of sea ice meltwater in the onset of autumn freeze up Crews, L., C.M. Lee, L. Rainville, and J. Thomson, "Direct observations of the role of lateral advection of sea ice meltwater in the onset of autumn freeze up," J. Geophys. Res., 127, doi:10.1029/2021JC017775, 2022. |
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1 Feb 2022 |
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In seasonally ice-free parts of the Arctic Ocean, autumn is characterized by heat loss from the upper ocean to the atmosphere and the onset of freeze up, in which first year sea ice begins to grow in open water areas. The timing of freeze up can be highly spatially variable, complicating efforts to provide accurate sea ice forecasting for marine operations. While melt season anomalies can be used to predict freeze up anomalies in some parts of the Arctic, this one-dimensional view merits further examination in light of recent work demonstrating the importance of three-dimensional flows in setting mixed layer properties in marginal ice zones. In this study, we show that horizontal advection of sea ice meltwater hastens freeze up in areas distant from the ice edge. We use nearly 800 temperature and salinity profiles along with satellite imagery collected in the central Beaufort Sea in autumn 2018 to document the roughly 100 km advection of a cold and fresh surface meltwater layer over several weeks. After the meltwater arrived, the mixed layer was cooler and shallower than the mixed layer in adjacent areas unaffected by the meltwater. The cooler and shallower meltwater-influenced mixed layer promoted earlier ice formation. Within the meltwater-affected area, advection was nearly as important as heat loss to the atmosphere for seasonally integrated mixed layer heat loss. |
Northern Ocean Rapid Surface Evolution (NORSE): Science and Experiment Plan Ballard, M., and 35 others including L. Rainville, L. Johnson, C. Lee, J. Shapiro, J. Thomson, and K. Zeiden, "Northern Ocean Rapid Surface Evolution (NORSE): Science and Experiment Plan," Technical Report, APL-UW TR 2102. Applied Physics Laboratory, University of Washington, January 2022, 40 pp. |
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13 Jan 2022 |
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The NORSE DRI focuses on characterizing the key physical parameters and processes that govern the predictability of upper-ocean rapid evolution events occurring in the ice-free high latitudes. The goal is to identify which observable parameters are most influential in improving model predictability through inclusion by assimilation, and to field an autonomous observing network that optimizes sampling of high-priority fields. The overall goal is to demonstrate improvements in the predictability of the upper ocean physical fields associated with acoustic propagation over the course of the study. This Science Plan describes the specific objectives and implementation plan. |
On the groupiness and intermittency of oceanic whitecaps Malila, M.P., J. Thomson, Ø. Breivik, A. Benetazzo, B. Scanlon, and B. Ward, "On the groupiness and intermittency of oceanic whitecaps," J. Geophys. Res., 127, doi:10.1029/2021JC017938, 2022. |
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8 Jan 2022 |
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The enhancement of wave breaking activity during wave group passage is investigated using coherent field observations of the instantaneous sea surface elevation and whitecap coverage from platform-based stereo video measurements in the central North Sea. Passing wave groups are shown to be associated with a two to three-fold enhancement in the probability distribution of total whitecap coverage W whereas the enhancement of active whitecap coverage WA is approximately five-fold. Breaking time scales and intermittency characteristics are also investigated with the inclusion of a secondary data set of W and WA observations collected during a research cruise in the North Pacific. The time scale analysis suggests a universal periodicity in wave breaking activity within a representative sea-surface area encompassing approximately one dominant wave crest. The breaking periodicity is shown to be closely linked to the peak period of the dominant wave components, suggesting that long-wave modulation of wave breaking is a predominant mechanism controlling the intermittency of wave breaking across scales. |
Landfast ice and coastal wave exposure in northern Alaska Hošeková, L., E. Eidam, G. Panteleev, L. Rainville, W.E. Rogers, and J. Thomson, "Landfast ice and coastal wave exposure in northern Alaska," Geophys. Res. Lett., 48, doi:10.1029/2021GL095103, 2021. |
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28 Nov 2021 |
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Observations of ocean surface waves at three sites along the northern coast of Alaska show a strong coupling with seasonal sea ice patterns. In the winter, ice cover is complete, and waves are absent. In the spring and early summer, sea ice retreats regionally, but landfast ice persists near the coast. The landfast ice completely attenuates waves formed farther offshore in the open water, causing up to two-month delay in the onset of waves nearshore. In autumn, landfast ice begins to reform, though the wave attenuation is only partial due to lower ice thickness compared to spring. The annual cycle in the observations is reproduced by the ERA5 reanalysis product, but the product does not resolve landfast ice. The resulting ERA5 bias in coastal wave exposure can be corrected by applying a higher resolution ice mask, and this has a significant effect on the long-term trends inferred from ERA5. |
Internal bore evolution across the shelf near Pt. Sal CA interpreted as a gravity current Spydell, M.S., and 15 others including C. Chickadel, M. Moulton, and J. Thomson, "Internal bore evolution across the shelf near Pt. Sal CA interpreted as a gravity current," J. Phys. Oceanogr., 51, 3629-3650, doi:10.1175/JPO-D-21-0095.1, 2021. |
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11 Nov 2021 |
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Off the central California coast near Pt. Sal, a large amplitude internal bore was observed for 20 h over 10 km cross-shore, or 100 m to 10 m water depth (D), and 30 km alongcoast by remote sensing, 39 in situ moorings, ship surveys, and drifters. The bore is associated with steep isotherm displacements representing a significant fraction of D. Observations were used to estimate bore arrival time tB, thickness h, and bore and non-bore (ambient) temperature difference ΔT, leading to reduced gravity g'. Bore speeds c, estimated from mapped tB, varied from 0.25 m s-1 to 0.1 m s-1 from D = 50 m to D = 10 m. The h varied from 5 to 35 m, generally decreased with D, and varied regionally alongisobath. The bore ΔT varied from 0.75 to 2.15°C. Bore evolution was interpreted from the perspective of a two-layer gravity current. Gravity current speeds U, estimated from the local bore h and g compared well to observed bore speeds throughout its cross-shore propagation. Linear internal wave speeds based on various stratification estimates result in larger errors. On average bore thickness h = D/2, with regional variation, suggesting energy saturation. From 5010 m depths, observed bore speeds compared well to saturated gravity current speeds and energetics that depend only on water depth and shelf-wide mean g'. This suggests that this internal bore is the internal wave analogue to a saturated surfzone surface gravity bore. Alongcoast variations in pre-bore stratification explain variations in bore properties. Near Pt. Sal, bore Doppler shifting by barotropic currents is observed. |
EUREC4A Stevens, B., and many others including K. Drushka, S. Iyer, and J. Thomson, "EUREC4A," Earth Syst. Sci. Data, 13, 4067-4119, doi:10.5194/essd-13-4067-2021, 2021. |
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25 Aug 2021 |
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The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement. |
Warm and cool nearshore plumes connecting the surf zone to the inner shelf Moulton, M., C.C. Chickadel, and J. Thomson, "Warm and cool nearshore plumes connecting the surf zone to the inner shelf," Geophys. Res. Lett., 48, doi:10.1029/2020GL091675, 2021. |
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28 May 2021 |
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Cross‐shore transport of larvae, pollutants, and sediment between the surf zone and the inner shelf is important for coastal water quality and ecosystems. Rip currents are known to be a dominant pathway for exchange, but the effects of horizontal temperature and salinity gradients are not well understood. Airborne visible and infrared imaging performed on the California coast shows warm and cool plumes driven by rip currents in the surf zone and extending onto the shelf, with temperature differences of approximately 1°C. The airborne imagery and modeled temperatures and tracers indicate that warm plumes exhibit more lateral spreading and transport material in a buoyant near‐surface layer, whereas cool plumes move offshore in a subsurface layer. The average cross‐shore extent of warm plumes at the surface is approximately one surfzone width larger than for cool plumes. Future work may explore the sensitivity of nearshore plumes to density patterns, wave forcing, and bathymetry. |
Rapid deterministic wave prediction using a sparse array of buoys Fisher, A., J. Thomson, and M. Schwendeman, "Rapid deterministic wave prediction using a sparse array of buoys," Ocean Eng., 228, doi:10.1016/j.oceaneng.2021.108871, 2021. |
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15 May 2021 |
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A long-standing problem in maritime operations and ocean development projects has been the prediction of instantaneous wave energy. Wave measurements collected using an array of freely drifting arrays of Surface Wave Instrument Float with Tracking (SWIFT) buoys are used to test methods for phase-resolved wave prediction in a wide range of observed sea states. Using a linear inverse model in directionally-rich, broadbanded wave fields can improve instantaneous heave predictions by an average of 63% relative to statistical forecasts based on wave spectra. Numerical simulations of a Gaussian sea, seeded with synthetic buoys, were used to supplement observations and characterize the spatiotemporal extent of reconstruction accuracy. Observations and numerical results agree well with theoretical deterministic prediction zones proposed in previous studies and suggest that the phase-resolved forecast horizon is between 13 average wave periods for a maximum measurement interval of 10 wave periods for ocean wave fields observed during the experiment. Prediction accuracy is dependent on the geometry and duration of the measurements and is discussed in the context of the nonlinearity and bandwidth of incident wave fields. |
The Inner-Shelf Dynamics Experiment Kumar, N., and 49 others, including J. Thomson, M. Moulton, and C. Chickadel, "The Inner-Shelf Dynamics Experiment," Bull. Am. Meteorol. Soc., 102, E1033–E1063, doi:10.1175/BAMS-D-19-0281.1, 2021. |
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1 May 2021 |
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The inner shelf, the transition zone between the surf zone and the mid shelf, is a dynamically complex region with the evolution of circulation and stratification driven by multiple physical processes. Cross-shelf exchange through the inner shelf has important implications for coastal water quality, ecological connectivity, and lateral movement of sediment and heat. The Inner-Shelf Dynamics Experiment (ISDE) was an intensive, coordinated, multi-institution field experiment from Sep.Oct. 2017, conducted from the mid shelf, through the inner shelf and into the surf zone near Point Sal, CA. Satellite, airborne, shore- and ship-based remote sensing, in-water moorings and ship-based sampling, and numerical ocean circulation models forced by winds, waves and tides were used to investigate the dynamics governing the circulation and transport in the inner shelf and the role of coastline variability on regional circulation dynamics. Here, the following physical processes are highlighted: internal wave dynamics from the mid shelf to the inner shelf; flow separation and eddy shedding off Point Sal; offshore ejection of surfzone waters from rip currents; and wind-driven subtidal circulation dynamics. The extensive dataset from ISDE allows for unprecedented investigations into the role of physical processes in creating spatial heterogeneity, and nonlinear interactions between various inner-shelf physical processes. Overall, the highly spatially and temporally resolved oceanographic measurements and numerical simulations of ISDE provide a central framework for studies exploring this complex and fascinating region of the ocean. |
Measurements from the RV Ronald H. Brown and related platforms as part of the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) Quinn, P.K., and 34 others including K. Drushka, S. Iyer, and J. Thomson, "Measurements from the RV Ronald H. Brown and related platforms as part of the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC)," Earth Syst. Sci. Data, 13, 1759-1790, doi:10.5194/essd-13-1759-2021, 2021. |
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29 Apr 2021 |
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The Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) took place from 7 January to 11 July 2020 in the tropical North Atlantic between the eastern edge of Barbados and 51°W, the longitude of the Northwest Tropical Atlantic Station (NTAS) mooring. Measurements were made to gather information on shallow atmospheric convection, the effects of aerosols and clouds on the ocean surface energy budget, and mesoscale oceanic processes. Multiple platforms were deployed during ATOMIC including the NOAA RV Ronald H. Brown (RHB) (7 January to 13 February) and WP-3D Orion (P-3) aircraft (17 January to 10 February), the University of Colorado's Robust Autonomous Aerial Vehicle-Endurant Nimble (RAAVEN) uncrewed aerial system (UAS) (24 January to 15 February), NOAA- and NASA-sponsored Saildrones (12 January to 11 July), and Surface Velocity Program Salinity (SVPS) surface ocean drifters (23 January to 29 April). The RV Ronald H. Brown conducted in situ and remote sensing measurements of oceanic and atmospheric properties with an emphasis on mesoscale oceanicatmospheric coupling and aerosolcloud interactions. In addition, the ship served as a launching pad for Wave Gliders, Surface Wave Instrument Floats with Tracking (SWIFTs), and radiosondes. Details of measurements made from the RV Ronald H. Brown, ship-deployed assets, and other platforms closely coordinated with the ship during ATOMIC are provided here. These platforms include Saildrone 1064 and the RAAVEN UAS as well as the Barbados Cloud Observatory (BCO) and Barbados Atmospheric Chemistry Observatory (BACO). Inter-platform comparisons are presented to assess consistency in the data sets. Data sets from the RV Ronald H. Brown and deployed assets have been quality controlled and are publicly available at NOAA's National Centers for Environmental Information (NCEI) data archive (https://www.ncei.noaa.gov/archive/accession/ATOMIC-2020, last access: 2 April 2021). Point-of-contact information and links to individual data sets with digital object identifiers (DOIs) are provided herein. |
A warm jet in a cold ocean MacKinnon, J.A., and 28 others including J. Thomson, S.D. Brenner, C.M. Lee, L. Rainville, and M.M. Smith, "A warm jet in a cold ocean," Nat. Commun., 12, doi:10.1038/s41467-021-22505-5, 2021. |
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23 Apr 2021 |
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Unprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre. |
Comparing observations and parameterizations of iceocean drag through an annual cycle across the Beaufort Sea Brenner, S., L. Rainville, J. Thomson, S. Cole, C. Lee, "Comparing observations and parameterizations of iceocean drag through an annual cycle across the Beaufort Sea," J. Geophys. Res., 126, doi:10.1029/2020JC016977, 2021. |
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1 Apr 2021 |
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Understanding and predicting sea ice dynamics and ice‐ocean feedback processes requires accurate descriptions of momentum fluxes across the ice‐ocean interface. In this study, we present observations from an array of moorings in the Beaufort Sea. Using a force‐balance approach, we determine ice‐ocean drag coefficient values over an annual cycle and a range of ice conditions. Statistics from high resolution ice draft measurements are used to calculate expected drag coefficient values from morphology‐based parameterization schemes. With both approaches, drag coefficient values ranged from approximately 110 x 10-3, with a minimum in fall and a maximum at the end of spring, consistent with previous observations. The parameterizations do a reasonable job of predicting the observed drag values if the under ice geometry is known, and reveal that keel drag is the primary contributor to the total ice‐ocean drag coefficient. When translations of bulk model outputs to ice geometry are included in the parameterizations, they overpredict drag on floe edges, leading to the inverted seasonal cycle seen in prior models. Using these results to investigate the efficiency of total momentum flux across the atmosphere‐ice‐ocean interface suggests an inter‐annual trend of increasing coupling between the atmosphere and the ocean. |
Long-term observations of the group structure of surface waves in ice Gemmrich, J., T. Mudge, and J. Thomson, "Long-term observations of the group structure of surface waves in ice," Ocean Dyn., 71, 343-356, doi:10.1007/s10236-020-01424-x, 2021. |
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1 Mar 2021 |
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Several years of surface wave observations in the Chukchi Sea reveal wave groups are a common feature in open water and ice-covered conditions. The strength of the groupiness, here characterized by the group factor, is well correlated with the characteristic wave steepness, the spectral bandwidth, and the Benjamin-Feir Index. The general finding is enhanced groupiness in ice. However, the trends with wave characteristics are opposite from ice to open water, and suggest different mechanisms. In ice, groupiness increases with decreasing steepness, increasing bandwidth, and decreasing Benjamin-Feir Index. In open water, the trends indicate that both linear superposition of phase-coherent waves and nonlinear behaviour are important for the generation of wave groups. We hypothesize that in ice-covered conditions, directional spreading reduces the effective bandwidth in the dominant wave direction, possibly due to modified four-wave nonlinear transfer spreading high-frequency energy to lateral directions. This reduced effective bandwidth is then conducive to enhanced group formation by linear superposition. However, an increased high-frequency noise floor of the in-ice observations would also be consistent with the observed increase in omni-directional bandwidth. Without directional measurements, neither of these two processes can be favoured with certainty. |
Spurious rollover of wave attenuation rates in sea ice caused by noise in field measurements Thomson, J., Hošeková, L., M.H. Meylan, A.L. Kohout, and N. Kumar, "Spurious rollover of wave attenuation rates in sea ice caused by noise in field measurements," J. Geophys. Res., 126, doi:10.1029/2020JC016606, 2021. |
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1 Mar 2021 |
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The effects of instrument noise on estimating the spectral attenuation rates of ocean waves in sea ice are explored using synthetic observations in which the true attenuation rates are known explicitly. The spectral shape of the energy added by noise, relative to the spectral shape of the true wave energy, is the critical aspect of the investigation. A negative bias in attenuation that grows in frequency is found across a range of realistic parameters. This negative bias decreases the observed attenuation rates at high frequencies, such that it can explain the rollover effect commonly reported in field studies of wave attenuation in sea ice. The published results from five field experiments are evaluated in terms of the noise bias, and a spurious rollover (or flattening) of attenuation is found in all cases. Remarkably, the wave heights are unaffected by the noise bias, because the noise bias occurs at frequencies that contain only a small fraction of the total energy. |
Wave-driven flow along a compact marginal ice zone Thomson, J., B. Lund, J. Hargrove, M.M. Smith, J. Horstmann, and J.A. MacKinnon, "Wave-driven flow along a compact marginal ice zone," Geophys. Res. Lett., 48, doi:10.1029/2020GL090735, 2021. |
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16 Feb 2021 |
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Observations of surface waves and ice drift along a compact sea ice edge demonstrate the importance of waves in a marginal ice zone. An analytic model is presented for the along‐ice drift forced by the radiation stress gradient of oblique waves. A momentum balance using quadratic drag to oppose the wave forcing is sufficient to explain the observations. Lateral shear stresses in the ice are also evaluated, though this balance does not match the observations as well. Additional forcing by local winds is included and is small relative to the wave forcing. However, the wave forcing is isolated to a narrow region around 500‐m wide, whereas the wind forcing has effects on larger scales. The simplistic drag is assessed using observations of shear and turbulent dissipation rates. The results have implications for the shape and evolution of the ice edge, because the lateral shear may be a source of instabilities. |
Attenuation of ocean surface waves in pancake and frazil sea ice along the coast of the Chukchi Sea Hošeková, L., M.P. Malila, W.E. Rogers, L.A. Roach, E. Eidam, L. Rainville, N. Kumar, and J. Thomson, "Attenuation of ocean surface waves in pancake and frazil sea ice along the coast of the Chukchi Sea," J. Geophys. Res., 125, doi:10.1029/2020JC016746, 2020. |
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1 Dec 2020 |
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Alaskan Arctic coastlines are protected seasonally from ocean waves by the presence of coastal and shorefast sea ice. This study presents field observations collected during the autumn 2019 freeze up near Icy Cape, a coastal headland in the Chukchi Sea of the Western Arctic. The evolution of the coupled air‐ice‐ocean‐wave system during a four‐day wave event was monitored using drifting wave buoys, a cross‐shore mooring array, and ship‐based measurements. The incident wave field with peak period of 2.5 s was attenuated by coastal pancake and frazil sea ice, reducing significant wave height by 40% over less than 5 km of cross‐shelf distance spanning water depths from 13 to 30 m. Spectral attenuation coefficients are evaluated with respect to wave and ice conditions and the proximity to the ice edge. Attenuation rates are found to be three times higher within 500 m of the ice edge, relative to values farther in the ice cover. Attenuation coefficients are in the range of <2.3,2.7> m-1, and follow a power‐law dependence on frequency. |
Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica Thompson, L., M. Smith, J. Thomson, S. Stammerjohn, S. Ackley, and B. Loose, "Frazil ice growth and production during katabatic wind events in the Ross Sea, Antarctica," Cryosphere, 14, 3329-3347, doi:10.5194/tc-14-3329-2020, 2020. |
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6 Oct 2020 |
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Katabatic winds in coastal polynyas expose the ocean to extreme heat loss, causing intense sea ice production and dense water formation around Antarctica throughout autumn and winter. The advancing sea ice pack, combined with high winds and low temperatures, has limited surface ocean observations of polynyas in winter, thereby impeding new insights into the evolution of these ice factories through the dark austral months. Here, we describe oceanic observations during multiple katabatic wind events during May 2017 in the Terra Nova Bay and Ross Sea polynyas. Wind speeds regularly exceeded 20 m s-1, air temperatures were below 25°C, and the oceanic mixed layer extended to 600 m. During these events, conductivity–temperature–depth (CTD) profiles revealed bulges of warm, salty water directly beneath the ocean surface and extending downwards tens of meters. These profiles reflect latent heat and salt release during unconsolidated frazil ice production, driven by atmospheric heat loss, a process that has rarely if ever been observed outside the laboratory. A simple salt budget suggests these anomalies reflect in situ frazil ice concentration that ranges from 13 to 266x10-3 kg m-3. Contemporaneous estimates of vertical mixing reveal rapid convection in these unstable density profiles and mixing lifetimes from 7 to 12 min. The individual estimates of ice production from the salt budget reveal the intensity of short-term ice production, up to 110 cm d-1 during the windiest events, and a seasonal average of 29 cm d-1. We further found that frazil ice production rates covary with wind speed and with location along the upstream–downstream length of the polynya. These measurements reveal that it is possible to indirectly observe and estimate the process of unconsolidated ice production in polynyas by measuring upper-ocean water column profiles. These vigorous ice production rates suggest frazil ice may be an important component in total polynya ice production. |
Long-term Measurements of Ocean Waves and Sea Ice Draft in the Central Beaufort Sea Thomson, J., "Long-term Measurements of Ocean Waves and Sea Ice Draft in the Central Beaufort Sea," Technical Memorandum, APL-UW TM 1-20, Applied Physics Laboratory, University of Washington, Seattle, 22 pp. |
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5 Oct 2020 |
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An ongoing program has measured ocean surface waves and sea ice draft at two sites in the Beaufort Sea (western Arctic Ocean) since 2012. This report presents the measurements and processed data products available from 2012 to 2018. Ocean surface waves are observed each summer and autumn when sea ice retreats; observed range of significant wave heights is 0.54 m. Sea ice is observed the rest of the year; observed range of average draft is 0.55 m. |
Pancake sea ice kinematics and dynamics using shipboard stereo video Smith, M., and J. Thomson, "Pancake sea ice kinematics and dynamics using shipboard stereo video," Ann. Glaciol., 61, 1-11, doi:10.1017/aog.2019.35, 2020. |
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1 Sep 2020 |
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In the marginal ice zone, surface waves drive motion of sea ice floes. The motion of floes relative to each other can cause periodic collisions, and drives the formation of pancake sea ice. Additionally, the motion of floes relative to the water results in turbulence generation at the interface between the ice and ocean below. These are important processes for the formation and growth of pancakes, and likely contribute to wave energy loss. Models and laboratory studies have been used to describe these motions, but there have been no in situ observations of relative ice velocities in a natural wave field. Here, we use shipboard stereo video to measure wave motion and relative motion of pancake floes simultaneously. The relative velocities of pancake floes are typically small compared to wave orbital motion (i.e. floes mostly follow the wave orbits). We find that relative velocities are well-captured by existing phase-resolved models, and are only somewhat over-estimated by using bulk wave parameters. Under the conditions observed, estimates of wave energy loss from iceocean turbulence are much larger than from pancake collisions. Increased relative pancake floe velocities in steeper wave fields may then result in more wave attenuation by increasing iceocean shear. |
A unified breaking onset criterion for surface gravity water waves in arbitrary depth Derakhti, M., J.T. Kirby, M.L. Banner, S.T. Grilli, and J. Thomson, "A unified breaking onset criterion for surface gravity water waves in arbitrary depth," J. Geophys. Res., 125, doi:10.1029/2019JC015886 |
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1 Jul 2020 |
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We investigate the validity and robustness of the Barthelemy et al. (2018, https://doi.org/10.1017/jfm.2018.93) wave‐breaking onset prediction framework for surface gravity water waves in arbitrary water depth, including shallow water breaking over varying bathymetry. We show that the Barthelemy et al. (2018) breaking onset criterion, which they validated for deep and intermediate water depths, also segregates breaking crests from nonbreaking crests in shallow water, with subsequent breaking always following the exceedance of their proposed generic breaking threshold. We consider a number of representative wave types, including regular, irregular, solitary, and focused waves, shoaling over idealized bed topographies including an idealized bar geometry and a mildly to steeply sloping planar beach. Our results show that the new breaking onset criterion is capable of detecting single and multiple breaking events in time and space in arbitrary water depth. Further, we show that the new generic criterion provides improved skill for signaling imminent breaking onset, relative to the available kinematic or geometric breaking onset criteria in the literature. In particular, the new criterion is suitable for use in wave‐resolving models that cannot intrinsically detect the onset of wave breaking. |
The evolution of a shallow front in the Arctic marginal ice zone Brenner, S., L. Rainville, J. Thomson, and C. Lee, "The evolution of a shallow front in the Arctic marginal ice zone," Elem. Sci. Anth., 8, doi:10.1525/elementa.413, 2020. |
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4 May 2020 |
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The high degree of heterogeneity in the iceoceanatmosphere system in marginal ice zones leads to a complex set of dynamics which control fluxes of heat and buoyancy in the upper ocean. Strong fronts may occur near the ice edge between the warmer waters of the ice-free regions and the cold, fresh waters near and under the ice. This study presents observations of a well-defined density front located along the ice edge in the Beaufort Sea. The evolution of the front over a ~3-day survey period is captured by multiple cross-front sections measured using an underway conductivitytemperaturedepth system, with simultaneous measurements of atmospheric forcing. Synthetic aperture radar images bookending this period show that the ice edge itself underwent concurrent evolution. Prior to the survey, the ice edge was compact and well defined while after the survey it was diffuse and filamented with coherent vortical structures. This transformation might be indicative of the development an active ocean eddy field in the upper ocean mixed layer. Over the course of hours, increasing wind stress is correlated with changes to the lateral buoyancy gradient and frontogenesis. Frontal dynamics appear to vary from typical open-ocean fronts (e.g., here the frontogenesis is linked to an "up-front" wind stress). Convective and shear-driven mixing appear to be unable to describe deepening at the heel of the front. While there was no measurable spatial variation in wind speed, we hypothesize that spatial heterogeneity in the total surface stress input, resulting from varying ice conditions across the marginal ice zone, may be a driver of the observed behaviour. |
Sparse sampling of intermittent turbulence generated by breaking surface waves Derakhti, M., J. Thomson, and J.T. Kirby, "Sparse sampling of intermittent turbulence generated by breaking surface waves," J. Phys. Oceanogr., 50, 867-885, doi:10.1175/JPO-D-19-0138.1, 2020. |
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1 Apr 2020 |
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We examine how Eulerian statistics of wave breaking and associated turbulence dissipation rates in a field of intermittent events compare with those obtained from sparse Lagrangian sampling by surface following drifters. We use a polydisperse two-fluid model with large-eddy simulation (LES) resolution and volume-of-fluid surface reconstruction (VOF) to simulate the generation and evolution of turbulence and bubbles beneath short-crested wave breaking events in deep water. Bubble contributions to dissipation and momentum transfer between the water and air phases are considered. Eulerian statistics are obtained from the numerical results, which are available on a fixed grid. Next, we sample the LES/VOF model results with a large number of virtual surface-following drifters that are initially distributed in the numerical domain, regularly or irregularly, before each breaking event. Time-averaged Lagrangian statistics are obtained using the time series sampled by the virtual drifters. We show that convergence of statistics occurs for signals that have minimum length of approximately 10003000 wave periods with randomly spaced observations in time and space relative to three-dimensional breaking events. We further show important effects of (i) extent of measurements over depth and (ii) obscuration of velocity measurements due to entrained bubbles, which are the two typical challenges in most of the available in situ observations of upper ocean wave breaking turbulence. An empirical correction factor is developed and applied to the previous observations of Thomson et al. Applying the new correction factor to the observations noticeably improves the inferred energy balance of wind input rates and turbulence dissipation rates. Finally, both our simulation results and the corrected observations suggested that the total wave breaking dissipation rates have a nearly linear relation with active whitecap coverage. |
LCDRI Field Experiment and Data Calibration Report Ma, B., E. D'Asaro, T. Sanford, J. Thomson, "LCDRI Field Experiment and Data Calibration Report," Technical Report, APL-UW TR 2002, Applied Physics Laboratory, University of Washington, Seattle, March 2020. |
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10 Mar 2020 |
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The goal of the Waves, Langmuir Cells and the Upper Ocean Boundary Layer Departmental Research Initiative (LCDRI) is to explore the upper ocean physics necessary to advance our understanding of the fluxes into and across the ocean mixed layer, including surface waves and wave breaking, Langmuir cells, and wavecurrent interaction. A set of comprehensive observational data was collected during the LCDRI field experiment from various platforms including autonomous floats, drifter, buoys, and shipboard observations. The field campaign was conducted on the coast of Southern California 21 March 5 April 2017. The fieldwork, including the event log and instrument deployment, is described in Part I. The inter-calibration between observed CTD data from EM-APEX and MLF floats, SWIFT drifters and R/V Sproul are described in Part II. For the MLF vs. EM-APEX calibration, the average salinity of MLF #82 and #83 top and bottom sensors is used as a reference. The calculated salinity offset for EM-APEX #6667, #6672, and #6678 is ~ 0.004 psu, for EM-APEX #6671 and #6674 is ~0.001 psu, and for EM-APEX #6675 is ~0.001 psu. For seven SWIFT drifters at 0.2, 0.5, and 1.2 m, the calculated temperature offset varies from 0.1 to 0.1°C and the salinity offset varies from 0.003 to 0.2 psu. The salinity data from SWIFT #16 and #17 at 0.2 m exhibited large offsets, which suggest data bias. The comparison of wave energy measurements between SWIFT drifters and a Datawell Waverider buoy moored at CDIP station 299 are described in Part III. Excluding the periods when the mean separation distance was greater than 30 km (periods 3−1, 3, 5, 6, 8, 12), the root-mean-square error (RMSE) of significant wave height (Hs) is 0.25 ± 0.08 m, the RMSE of integrated wave energy is 0.057 ± 0.029 m2, and the average percent error of Hs is ~13%. In general, given the temporal, spatial, and spectral differences in the sampling strategy of SWIFTdrifters and the CDIP buoy, the comparison suggests no significant bias in either dataset. |
A conceptual model of a river plume in the surf zone Kastler, S.E., A.R. Horner-Devine, and J.M. Thomson, "A conceptual model of a river plume in the surf zone," J. Geophys. Res., 124, 8060-8078, doi:10.1029/2019JC015510, 2019. |
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1 Nov 2019 |
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We use observations from the Quinault River, a small river that flows into an energetic surf zone on the West Coast of Washington state, to investigate the interaction between river and wave forcing. By synthesizing data from moorings, drifters, and Unmanned Aerial System video, we develop a conceptual model of this interaction based on three length scales: the surf zone width, LSZ; the near‐field plume length, LNF; and the cross‐shore extent of the channel, LC. The relationships between these length scales show how tidal variability and bathymetric effects change the balance of wave and river momentum. The most frequently observed state is LSZ>LNF. Under these conditions the surf zone traps the outflowing river plume and the river water's initial propagation into the surf zone is set by LNF. When the river velocity is highest during low water, and when wave forcing is low, LNF>LSZ and river water escapes the surf zone. At high water during low wave forcing, LC>LSZ, such that minimal wave breaking occurs in the channel and river water escapes onto the shelf. Based on the discharge, wave, and tidal conditions, the conceptual model is used to predict the fate of river water from the Quinault over a year, showing that approximately 70% of the river discharge is trapped in the surf zone upon exiting the river mouth. |
Impact of swell on the wind-sea and resulting modulation of stress Vincent, C.L., J. Thomson, H.C. Graber, and C.O. Collins III, "Impact of swell on the wind-sea and resulting modulation of stress," Prog. Oceanogr., 178, 102164, doi:10.1016/j.pocean.2019.102164, 2019. |
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1 Nov 2019 |
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Wave groups observed in pancake sea ice Thomson, J., J. Gemmrich, W.E. Rogers, C.O. Collins, and F. Ardhuin, "Wave groups observed in pancake sea ice," J. Geophys. Res., 124, 7400-7411, doi:10.1029/2019JC015354, 2019. |
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1 Nov 2019 |
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Ocean surface waves propagating through sea ice are scattered and dissipated. The net attenuation occurs preferentially at the higher frequencies, and thus the spectral bandwidth of a given wave field is reduced, relative to open water. The reduction in bandwidth is associated with an increase in the groupiness of the wave field. Using SWIFT buoy data from the 2015 Arctic Sea State experiment, bandwidth is compared between pancake ice and open water conditions, and the linkage to group envelopes is explored. The enhancement of wave groups in ice is consistent with the simple linear mechanism of superposition of waves with narrowing spectral bandwidth. This is confirmed using synthetic data. Nonlinear mechanisms, which have been shown as significant in other ice types, are not found to be important in this data set. |
Breaking waves in deep water: Measurements and modeling of energy dissipation Rollano, F.T., A. Brown, A. Ellenson, H.T. Özkan-Haller, J. Thomson, and M.C. Haller, "Breaking waves in deep water: Measurements and modeling of energy dissipation," Ocean Dyn., 69, 1165-1179, doi:10.1007/s10236-019-01301-2, 2019. |
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1 Oct 2019 |
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In the presence of strong winds, ocean surface waves dissipate significant amounts of energy by breaking. Here, breaking rates and wave-following turbulent dissipation rate measurements are compared with numerical WAVEWATCH III estimates of bulk energy dissipation rate. At high winds, the measurements suggest that turbulent dissipation becomes saturated; however, the modeled bulk dissipation continues to increase as a cubic function of wind speed. Similarly, the mean square slope (i.e., the steepness) of the measured waves becomes saturated, while the modeled mean squared slope grows linearly with wind speed. Only a weak relation is observed between breaker fraction and wind speed, possibly because these metrics do not capture the scale (e.g., crest length) of the breakers. Finally, the model skill for basic parameters such as significant wave height is shown to be sensitive to the dissipation rate, indicating that the model skill may be compromised under energetic conditions. |
Kinematics and statistics of breaking waves observed using SWIFT buoys Brown, A., J. Thomson, A. Ellenson, F.T. Rollano, H.T. Özkan-Haller, and M.C. Haller, "Kinematics and statistics of breaking waves observed using SWIFT buoys," IEEE J. Ocean. Eng., 44, 1011-1023, doi:10.1109/JOE.2018.2868335, 2019. |
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1 Oct 2019 |
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Surface wave instrumentation floats with tracking were deployed by helicopter ahead of five large storms off the Oregon coast. The buoys drifted freely with the wave motions, surface currents, and wind. The buoys use a 9-DoF inertial measurement unit that fuses the measurements of accelerometers, magnetometers, and gyroscopes to measure acceleration in the global North-West-Up reference frame. Rapid sampling (25 Hz) allows for the observation of both propagating wave motions and wave breaking events. Bulk wave parameters and wave spectra are calculated from the motion of the buoys using conventional methods, and breaking wave impacts are identified in the raw acceleration data using a new algorithm based on a short-time Fourier transform. The number of breaking waves is used to infer breaker fraction, which is found to depend on bulk wave steepness as previously shown in the literature. The magnitude and duration of acceleration during breaking is used in a new quantification of breaker intensity, which increases with wave height, period, and steepness. There is significant variance of breaker intensity in a given wave field, such that intense breakers still occur in relatively mild wave fields. The buoy observations are compared to the output of the WaveWatch III forecast model, with evaluation of an empirical breaker prediction scheme applied to WaveWatch III output. |
Kinematics and statistics of breaking waves observed using SWIFT buoys Brown, A., J. Thomson, A. Ellenson, F.T. Rollano, H.T. Özkan-Haller, and M.C. Haller, "Kinematics and statistics of breaking waves observed using SWIFT buoys," IEEE J. Ocean. Eng., 44, 1011-1023, doi:10.1109/JOE.2018.2868335, 2019. |
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1 Oct 2019 |
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Surface wave instrumentation floats with tracking were deployed by helicopter ahead of five large storms off the Oregon coast. The buoys drifted freely with the wave motions, surface currents, and wind. The buoys use a 9-DoF inertial measurement unit that fuses the measurements of accelerometers, magnetometers, and gyroscopes to measure acceleration in the global North-West-Up reference frame. Rapid sampling (25 Hz) allows for the observation of both propagating wave motions and wave breaking events. Bulk wave parameters and wave spectra are calculated from the motion of the buoys using conventional methods, and breaking wave impacts are identified in the raw acceleration data using a new algorithm based on a short-time Fourier transform. The number of breaking waves is used to infer breaker fraction, which is found to depend on bulk wave steepness as previously shown in the literature. The magnitude and duration of acceleration during breaking is used in a new quantification of breaker intensity, which increases with wave height, period, and steepness. There is significant variance of breaker intensity in a given wave field, such that intense breakers still occur in relatively mild wave fields. The buoy observations are compared to the output of the WaveWatch III forecast model, with evaluation of an empirical breaker prediction scheme applied to WaveWatch III output. |
Constraining Southern Ocean airseaice fluxes through enhanced observations Swart, S., and 19 others including J. Thomson and J. Girton, "Constraining Southern Ocean airseaice fluxes through enhanced observations," Front. Mar. Sci., 6, 421, doi:10.3389/fmars.2019.00421, 2019. |
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31 Jul 2019 |
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Airsea and airseaice fluxes in the Southern Ocean play a critical role in global climate through their impact on the overturning circulation and oceanic heat and carbon uptake. The challenging conditions in the Southern Ocean have led to sparse spatial and temporal coverage of observations. This has led to a 'knowledge gap' that increases uncertainty in atmosphere and ocean dynamics and boundary-layer thermodynamic processes, impeding improvements in weather and climate models. Improvements will require both process-based research to understand the mechanisms governing air-sea exchange and a significant expansion of the observing system. This will improve flux parameterizations and reduce uncertainty associated with bulk formulae and satellite observations. Improved estimates spanning the full Southern Ocean will need to take advantage of ships, surface moorings, and the growing capabilities of autonomous platforms with robust and miniaturized sensors. A key challenge is to identify observing system sampling requirements. This requires models, Observing System Simulation Experiments (OSSEs), and assessments of the specific spatial-temporal accuracy and resolution required for priority science and assessment of observational uncertainties of the mean state and direct flux measurements. Year-round, high-quality, quasi-continuous in situ flux measurements and observations of extreme events are needed to validate, improve and characterize uncertainties in blended reanalysis products and satellite data as well as to improve parameterizations. Building a robust observing system will require community consensus on observational methodologies, observational priorities, and effective strategies for data management and discovery. |
Waves and swell in high wind and extreme fetches, measurement in the Southern Ocean Babanin, A.V., and 21 others including J. Thomson, "Waves and swell in high wind and extreme fetches, measurement in the Southern Ocean," Front. Mar. Sci., 6, doi:10.3389/fmars.2019.00361, 2019. |
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9 Jul 2019 |
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The generation and evolution of ocean waves by wind is one of the most complex phenomena in geophysics, and is of great practical significance. Predictive capabilities of respective wave models, however, are impaired by lack of field in situ observations, particularly in extreme Metocean conditions. The paper outlines and highlights important gaps in understanding the Metocean processes and suggests a major observational program in the Southern Ocean. This large, but poorly investigated part of the World Ocean is home to extreme weather around the year. The observational network would include distributed system of buoys (drifting and stationary) and autonomous surface vehicles (ASV), intended for measurements of waves and air-sea fluxes in the Southern Ocean. It would help to resolve the issues of limiting fetches, extreme Extra-Tropical cyclones, swell propagation and attenuation, wavecurrent interactions, and address the topics of wave-induced dispersal of floating objects, waveice interactions in the Marginal Ice Zone, Metocean climatology and its connection with the global climate. |
Wave attenuation by sea ice turbulence Voermans, J.J., A.V. Babanin, J. Thomson, M.M. Smith, and H.H. Shen, "Wave attenuation by sea ice turbulence," Geophys. Res. Lett., 46, 6796-6803, doi:10.1029/2019GL082945, 2019. |
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28 Jun 2019 |
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The dissipation of wave energy in the marginal ice zone is often attributed to wave scattering and the dissipative mechanisms associated with the ice layer. In this study we present observations indicating that turbulence generated by the differential velocity between the sea ice cover and the orbital wave motion may be an important dissipative mechanism of wave energy. Through field measurements of under‐ice turbulence dissipation rates in pancake and frazil ice, it is shown that turbulence‐induced wave attenuation coefficients are in agreement with observed wave attenuation in the marginal ice zone. The results suggest that the turbulence‐induced attenuation rates can be parameterized by the characteristic wave properties and a coefficient. The coefficient is determined by the ice layer properties. |
Tidal current observations through Admiralty Inlet from ferry-mounted current profilers Guerra, M., J. Thomson, T. Prusa, C. Falkenhayn Maloy, C. Krembs, and B. Sackmann, "Tidal current observations through Admiralty Inlet from ferry-mounted current profilers," J. Ocean Eng. Mar. Energy, 5, 159-172, doi:10.1007/s40722-019-00135-w, 2019. |
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1 May 2019 |
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Admiralty Inlet is a narrow sill located at the northern end of Puget Sound (WA, USA). Circulation through Admiralty Inlet is complex, with tidal currents exceeding 3 m s-1, large variations in fresh water input to the system, and seasonal ocean water intrusions. Long-term observations of the currents across the entire inlet are crucial for understanding circulation through Puget Sound. In this context, the Washington State Department of Transportation (WSDOT) Ferries, which run year round through Admiralty Inlet, provide a cost-effective platform to mount instruments and obtain long time series of currents distributed across the inlet. Through the Ferry-Base Monitoring of Puget Sound Currents project, two down-looking acoustic Doppler current profilers (ADCPs) are installed on board two WSDOT ferries, providing depth profiles of velocities across the inlet since May 2014. All data are quality controlled and organized in an horizontal and vertical grid across the inlet. Data within each grid cell are analyzed to capture tidal current harmonic components. Results agree well with data from fixed bottom-mounted ADCPs, and show large spatial variability in the amplitude of harmonic components, probably related to the bathymetric features of the inlet. Further analysis provides estimates of tidal asymmetry and residual currents through the inlet, which are relevant to water quality within the Puget Sound. |
Maximum wave heights from global model reanalysis Barbariol, F., J.-R. Bidlot, L. Cavaleri, M. Sclavo, J. Thomson, and A. Benetazzo, "Maximum wave heights from global model reanalysis," Prog. Oceanogr., 175, 139-160, doi:10.1016/j.pocean.2019.03.009, 2019. |
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27 Mar 2019 |
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Very large waves populate the world oceans and challenge seafarers and offshore structures, but their long-term and global assessment is uneasy because of the scarcity of observations and their narrow time-coverage. Modern model reanalysis datasets with high spatio-temporal extent and resolution represent a valuable tool for this scope. In this paper, we use for the first time reanalysis datasets to provide a long-term and global statistical assessment of the maximum wave parameters, namely crest, crest-to-trough and envelope heights. In particular, we rely on the ERA-Interim directional wave spectra that are used to estimate the parameters of the probability distributions of wave maxima. To represent the customary single-point observations we use time extreme statistical models, while to account for the three-dimensional geometry and short-crestedness of stormy ocean waves, the statistical models are extended to space-time. In order to evaluate the accuracy of the reanalysis-based wave maxima estimates we verify them against buoy and stereo-video wave observations gathered in the North Pacific Ocean. We then provide the global assessment of maximum crest, crest-to-trough and envelope heights during typical and extreme conditions, showing the regions attaining the largest values, which we show are located in the mid-latitude storm belts, in particular in the North Atlantic Ocean. With respect to previous wave climate studies that focused on the significant wave height only, in this study we quantify the maximum wave height extent, also highlighting the role of mean wave steepness and kurtosis (measures of nonlinearity) and spectral bandwidth (measure of irregularity). Beside this, we show that the contribution of the short-crestedness is significant and that taking it into account may be relevant for the safety of navigation, ship routing and marine structural design. |
A new version of the SWIFT platform for waves, currents, and turbulence in the ocean surface layer Thomson, J., M. Moulton, A. de Klerk, J. Talbert, M. Guerra, S. Kastner, M. Smith, M. Schwendeman, S. Zippel, and S. Nylund, "A new version of the SWIFT platform for waves, currents, and turbulence in the ocean surface layer," Proc., IEEE/OES 12th Currents, Waves, Turbulence Measurement and Applications Workshop, 10-13 March, San Diego, CA (IEEE, 2019). |
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10 Mar 2019 |
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The Surface Wave Instrument Float with Tracking (SWIFT) is a freely drifting platform for measurements of waves, currents, and turbulence in the ocean surface layer. This platform |
Ocean surface turbulence in newly formed marginal ice zones Smith, M., and J. Thomson, "Ocean surface turbulence in newly formed marginal ice zones," J. Geophys. Res., 124, 1382-1398, doi:10.1029/2018JC014405, 2019. |
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1 Mar 2019 |
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Near‐surface turbulent kinetic energy dissipation rates are altered by the presence of sea ice in the marginal ice zone, with significant implications for exchanges at the air‐ice‐ocean interface. Observations spanning a range of conditions are used to parameterize dissipation rates in marginal ice zones with relatively thin, newly formed ice, and two regimes are identified. In both regimes, the turbulent dissipation rates are matched to the turbulent input rate, which is formulated as the surface stress acting on roughness elements moving at an effective transfer velocity. In marginal ice zones with waves, the short waves are the roughness elements, and the phase speed of these waves is the effective transfer velocity. The wave amplitudes are attenuated by the ice, and thus, the size of the roughness elements is reduced; this is parameterized as a reduction in the effective transfer velocity. When waves are sufficiently small, the ice floes are the roughness elements, and the relative velocity between the sea ice and the ocean is the effective transfer velocity. A scaling is introduced to determine the appropriate transfer velocity in a marginal ice zone based on wave height, ice thickness and concentration, and ice‐ocean shear. The results suggest that turbulence underneath new sea ice is mostly related to the wind forcing and that marginal ice zones generally have less turbulence than the open ocean under similar wind forcing. |
Wake measurements from a hydrokinetic river turbine Guerra, M., and J. Thomson, "Wake measurements from a hydrokinetic river turbine," Renewable Energy, 139, 483-495, doi:10.1016/j.renene.2019.02.052, 2019. |
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15 Feb 2019 |
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During the boreal summer of 2015, a full-scale hydrokinetic turbine was deployed in the Kvichak River (Alaska), delivering electricity to the village of Igiugig. Here, quantification and analysis of the hydrodynamic modifications in the river caused by the turbine are presented. Field observations are used to produce a unique three-dimensional data set of fluid velocities in the vicinity of the turbine before and after turbine deployment. Three dynamic regions are distinguished in the wake. There is an induction zone just upstream of the turbine, where velocities decrease and turbulence increases. There is a near wake just downstream of the turbine, where the reduced velocities recover slightly and the elevated turbulence decays rapidly. Finally, there is a far wake well beyond the turbine, where reduced velocities are persistent and turbulence remains elevated. The results are used in a coarse energy budget for the river, including quantifying the total energy dissipated by turbulence in the near wake. This wake dissipation is found to be almost as large as the energy extracted for electricity generation, even when the turbine is not operational. |
Overview of the Arctic Sea State and Boundary Layer Physics Program Thomson, J., and 32 others, including L. Rainville, and M. Smith, "Overview of the Arctic Sea State and Boundary Layer Physics Program," J. Geophys. Res., 123, 8674-8687, doi:10.1002/2018JC013766, 2018. |
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1 Dec 2018 |
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A large collaborative program has studied the coupled air‐ice‐ocean‐wave processes occurring in the Arctic during the autumn ice advance. The program included a field campaign in the western Arctic during the autumn of 2015, with in situ data collection and both aerial and satellite remote sensing. Many of the analyses have focused on using and improving forecast models. Summarizing and synthesizing the results from a series of separate papers, the overall view is of an Arctic shifting to a more seasonal system. The dramatic increase in open water extent and duration in the autumn means that large surface waves and significant surface heat fluxes are now common. When refreezing finally does occur, it is a highly variable process in space and time. Wind and wave events drive episodic advances and retreats of the ice edge, with associated variations in sea ice formation types (e.g., pancakes, nilas). This variability becomes imprinted on the winter ice cover, which in turn affects the melt season the following year. |
A surface kinematics buoy (SKIB) for wavecurrent interaction studies Guimarães, P.V., F. Ardhuin, P. Sutherland, M. Accensi, M. Hamon, Y. Pérignon, J. Thomson, A. Benetazzo, and P. Ferrant, "A surface kinematics buoy (SKIB) for wavecurrent interaction studies," Ocean Sci., 14, 1449-1460, doi:10.5194/os-14-1449-2018, 2018. |
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26 Nov 2018 |
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Global navigation satellite systems (GNSSs) and modern motion-sensor packages allow the measurement of ocean surface waves with low-cost drifters. Drifting along or across current gradients provides unique measurements of wavecurrent interactions. In this study, we investigate the response of several combinations of GNSS receiver, motion-sensor package and hull design in order to define a prototype "surface kinematics buoy" (SKIB) that is particularly optimized for measuring wavecurrent interactions, including relatively short wave components that are important for airsea interactions and remote-sensing applications. The comparison with existing Datawell Directional Waverider and Surface Wave Instrument Float with Tracking (SWIFT) buoys, as well as stereo-video imagery, demonstrates the performance of SKIB. The use of low-cost accelerometers and a spherical ribbed and skirted hull design provides acceptable heave spectra E(f) from 0.09 to 1 Hz with an acceleration noise level (2πf)4E(f) close to 0.023 m2 s-3. Velocity estimates from GNSS receivers yield a mean direction and directional spread. Using a low-power acquisition board allows autonomous deployments over several months with data transmitted by satellite. The capability to measure current-induced wave variations is illustrated with data acquired in a macro-tidal coastal environment. |
Hydrodynamic coefficients of heave plates, with application to wave energy conversion Brown, A., J. Thomson, and C. Rusch, "Hydrodynamic coefficients of heave plates, with application to wave energy conversion," IEEE J. Ocean. Eng., 43, 983-996, doi:10.1109/JOE.2017.2762258, 2018. |
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1 Oct 2018 |
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Wave energy converters (WECs) often employ submerged heave plates to provide reaction forces at depths below the level of wave motion. Here, two sets of heave plate experiments are described, at varying scale. First, the Oscillator uses a linear actuator to force laboratory scale (30.5-cm diameter) heave plates in sinusoidal motion. Second, the miniWEC buoy uses vessel wakes to force field scale (1.5-m diameter) heave plates in open water with realistic energy conversion (damping). The motion and forces are analyzed using the Morison equation, in which the hydrodynamic coefficients of added mass CM and drag CD are determined for each set of Oscillator and miniWEC experiments. Results show strong intracycle variations in these coefficients, yet constant hydrodynamic coefficients provide a reasonable reconstruction of the time series data. The two test scales are examined relative to the KeuleganCarpenter number (KC), Reynold's number (Re), and Beta number (β). The effects of asymmetric shape on hydrodynamic performance are found to be small. |
The influence of wind and waves on spreading and mixing in the Fraser River plume Kastner, S.E., A.R. Horner-Devine, and J. Thomson, "The influence of wind and waves on spreading and mixing in the Fraser River plume," J. Geophys. Res., 123, 6818-6840, doi:10.1029/2018JC013765, 2018. |
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5 Sep 2018 |
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This study uses drifter‐based observations to investigate the role of wind and waves on spreading and mixing in the Fraser River plume. Local winter wind patterns commonly result in two distinct forcing conditions, moderate winds from the southeast (SE) and strong winds from the northwest (NW). We examine how these patterns influence the spreading and mixing dynamics of the plume. Under SE winds, the plume thins, spreads, and turns to the right (north) upon exiting the river mouth. Mixing is initially intense in the region of maximum spreading, but it is short‐lived. Under NW winds, which oppose the rightward tendency of the plume, the plume remains thicker, narrower, and flows directly across the Strait with a lateral front on its northern side. Mixing is initially lower than under SE forcing but persists further across the Strait. A Lagrangian stream‐normal momentum balance shows that wind and interfacial stress under NW conditions compress the sea surface height anomaly formed by the river discharge and guide the flow across the Strait. This reconfiguration changes spreading and mixing dynamics of the plume; plume spreading, which drives intense mixing under SE winds, is shut down under NW winds, and mixing rates are consequently much lower. Despite the initially lower mixing rates, the region of active mixing extends further under NW winds, resulting in higher net mixing. These results highlight that the wind, which is often a primary cause of increased plume mixing, can also significantly influence mixing by changing the geometry of the plume. |
Attenuation and directional spreading of ocean waves during a storm event in the autumn Beaufort Sea marginal ice zone Montiel, F., V.A. Squire, M. Doble, J. Thomson, and P. Wadhams, "Attenuation and directional spreading of ocean waves during a storm event in the autumn Beaufort Sea marginal ice zone," J. Geophys. Res., 123, 5912-5932, doi:10.1029/2018JC013763, 2018. |
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1 Aug 2018 |
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This paper investigates the attenuation and directional spreading of large amplitude waves traveling through pancake ice. Directional spectral density is analyzed from in situ wave buoy data collected during a 3‐day storm event in October 2015 in the Beaufort Sea. Two proxy metrics for wave amplitude obtained from energy density spectra, namely, spectral amplitude and significant wave height, are used to track the waves as they propagate along transects through the array of buoys in the predominantly pancake ice field. Two types of wave buoys are used in the analysis and compared, exhibiting significant differences in the wave energy density and directionality estimates. Although exponential decay is observed predominantly, one of the two buoy types indicates a potential positive correlation between wave energy density and the occurrence of linear wave decay, as opposed to exponential decay, in accord with recent observations in the Antarctic marginal ice zone. Factors affecting the validity of this observation are discussed. An empirical power law with exponent 2.2 is also found to hold between the exponential attenuation coefficient and wave frequency. The directional content of the wave spectrum appears to decrease consistently along the wave transects, confirming that wave energy is being dissipated by the pancake ice as opposed to being scattered by ice cakes. |
On the ocean wave attenuation rate in grease-pancake ice, a comparison of viscous layer propagation models with field data De Santi, F., G. De Carolis, P. Olla, M. Doble, S. Cheng, H.H. Shen, P. Wadhams, and J. Thomson, "On the ocean wave attenuation rate in grease-pancake ice, a comparison of viscous layer propagation models with field data," J. Geophys. Res., 123, 5933-5948, doi:10.1029/2018JC013865, 2018. |
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1 Aug 2018 |
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The ability of viscous layer models to describe the attenuation of waves propagating in grease‐pancake ice covered ocean is investigated. In particular, the Keller's model (Keller, 1998; https://doi.org/10.1029/97JC02966), the two‐layer viscous model (De Carolis & Desiderio, 2002; https://doi.org/10.1016/S0375-9601(02)01503-7) and the close‐packing model (De Santi & Olla, 2017; arXiv:1512.05631) are extensively validated by using wave attenuation data collected during two different field campaigns (Weddell Sea, Antarctica, April 2000; western Arctic Ocean, autumn 2015). We use these data to inspect the performance of the three models by minimizing the differences between the measured and model wave attenuation; the retrieved ice thickness is then compared with measured data. The three models allow to fit the observation data but with important differences in the three cases. The close‐packing model shows good agreement with the data for values of the ice viscosity comparable to those of grease ice in laboratory experiments. For thin ice, the Keller's model performance is similar to that of the close‐packing model, while for thick ice much larger values of the ice viscosity are required, which reflects the different ability of the two models to take into account the effect of pancakes. The improvement of performance over the Keller's model achieved by the two‐layer viscous model is minimal, which reflects the marginal role in the dynamics of a finite eddy viscosity in the ice‐free layer. A good ice thickness retrieval can be obtained by considering the ice layer as the only source in the wave dynamics, so that the wind input can be disregarded. |
Wave attenuation through an Arctic marginal ice zone on 12 October 2015: 2. Numerical modeling of waves and associated ice breakup Ardhuin, F., G. Boutin, J. Stopa, F. Girard‐Ardhuin, C. Melsheimer, J. Thomson, A. Kohout, M. Doble, and P. Wadhams, "Wave attenuation through an Arctic marginal ice zone on 12 October 2015: 2. Numerical modeling of waves and associated ice breakup," J. Geophys. Res., 123, 5652-5668, doi:10.1002/2018JC013784, 2018. |
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1 Aug 2018 |
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Many processes that affect ocean surface gravity waves in sea ice give rise to attenuation rates that vary with both wave frequency and amplitude. Here we particularly test the possible effects of basal friction, scattering by ice floes, and dissipation in the ice layer due to dislocations, and ice breakup by the waves. The possible influence of these processes is evaluated in the marginal ice zone of the Beaufort Sea, where extensive wave measurements were performed. The wave data includes in situ measurements and the first kilometer‐scale map of wave heights provided by Sentinel‐1 SAR imagery on 12 October 2015, up to 400 km into the ice. We find that viscous friction at the base of an ice layer gives a dissipation rate that may be too large near the ice edge, where ice is mostly in the form of pancakes. Further into the ice, where larger floes are present, basal friction is not sufficient to account for the observed attenuation. In both regions, the observed narrow directional wave spectra are consistent with a parameterization that gives a weak effect of wave scattering by ice floes. For this particular event, with a dominant wave period around 10 s, we propose that wave attenuation is caused by ice flexure combined with basal friction that is reduced when the ice layer is not continuous. This combination gives realistic wave heights, associated with a 100200 km wide region over which the ice is broken by waves, as observed in SAR imagery. |
Wave evolution in off-ice wind conditions Gemmrich, J., W.E. Rogers, J. Thomson, S. Lehner, "Wave evolution in off-ice wind conditions," J. Geophys. Res., 123, 5543-5556, doi:10.1029/2018JC013793, 2018. |
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1 Aug 2018 |
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The reduction of the sea ice coverage increases the importance of wind waves in the Arctic. Updates to the standard spectral wave models in recent years have included many aspects of waveice interaction. Here we use high‐resolution wave parameters retrieved from TerraSAR‐X images and in situ SWIFT buoy observations to evaluate the performance of WAVEWATCH III® in ice‐free waters in the western Arctic over a 7‐week period including the fall freeze‐up. About two thirds of the analyzed data sets show a good agreement between observations and model results. In other cases, more accurate representation of the wind input fields and the ice coverage could improve the model predictions. Two data sets with larger discrepancy are discussed in more detail. In these two cases of low model skill, with off‐ice wind conditions, we show that the model wind‐sea growth is too weak to match TerraSAR‐X observations, and this situation is improved only slightly by including the effects of atmospheric stability using existing methods. Application of an effective fetch parameterization, which allows for reduced wave generation within the marginal ice zone prior to the open ocean, provides the best estimation of wave growth during off‐ice winds. |
Shipboard observations of the meteorology and near-surface environment during autumn freeze-up in the Beaufort/Chukchi seas Persson, P.O.G., B. Blomquist, P. Guest, S. Stammerjohn, C. Fairall, L. Rainville, B. Lund, S. Ackley, and J. Thomson, "Shipboard observations of the meteorology and near-surface environment during autumn freeze-up in the Beaufort/Chukchi seas," J. Geophys. Res., 123, 4930-4969, doi:10.1029/2018JC013786, 2018. |
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1 Jul 2018 |
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The collection and processing of shipboard air, ice, and ocean measurements from the Sea State field campaign in the Beaufort/Chukchi Seas in autumn 2015 are described and the data used to characterize the near‐surface freezeup environment. The number of parameters measured or derived is large and the location and time of year are unique. Analysis was done of transits through the new, growing ice and of ice edge periods. Through differential surface energy fluxes, the presence of new, thin sea ice (<50 cm) produces lower tropospheric air temperatures in the ice interior that average ~4°C colder than those over open water near the ice edge, resulting in an ice edge baroclinic zone. This temperature difference doubles by late October and produces thermodynamic and dynamic feedbacks. These include off‐ice, cold‐air advection leading to enhanced surface heat loss averaging ~200 W/m2 over the open water, formation of low‐level jets, suppression of the ice edge baroclinic zone, and enhanced ice drift. The interior ice growth rate is thermodynamically consistent with a surface heat loss of ~65 W/m2 to the atmosphere and a heat flux of several tens of W/m2 from the ocean below. Ice drift at times contributes to the southward advance of the autumn ice edge through off‐ice winds. The ocean thermohaline structure is highly variable and appears associated with bathymetric features, small‐scale upper‐ocean eddies, and the growing ice cover. Lower salinity under the ice interior compared to the nearby ice edge is an upper‐ocean impact of this thin ice cover. |
Rich Passage Tidal Energy Resource Characterization Guerra, M., and J. Thomson, "Rich Passage Tidal Energy Resource Characterization," Technical Memorandum, APL-UW TM 2-18, Applied Physics Laboratory, University of Washington, Seattle, June 2018, 17 pp. |
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27 Jun 2018 |
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Current and wave measurements were taken in Rich Passage in Puget Sound, WA, during fall 2014. Two instruments were deployed at the west end of Rich Passage; one measured currents and the other measured both currents and waves. The main objectives of the study were to measure waves generated by vessels transiting Rich Passage and to quantify the tidal energy resource of the channel. This report presents the analysis of the measured currents and an assessment of the hydrokinetic power available in Rich Passage. |
Wave Energy Resource Characterization for San Nicholas Island Johnson, N., and J. Thomson, "Wave Energy Resource Characterization for San Nicholas Island," Technical Memorandum, APL-UW TM 3-18, Applied Physics Laboratory, University of Washington, Seattle, June 2018, 37 pp. |
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27 Jun 2018 |
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To characterize the wave energy resource for San Nicolas Island, off the coast of Southern California, wave data collected on three buoys located near the island were assembled from the Coastal Data Information Program (CDIP). These data were used to create joint probability density function plots and monthly-averaged plots of bulk parameters and energy spectra. Observed monthly-averaged bulk parameters and calculated power densities were compared to a wave energy atlas created by the National Renewable Energy Laboratory (NREL). Wave climatology products available from the Global Spectral Wave Climate (GLOSWAC) program were also compared with the climatology derived from the buoy data. Finally, regional spatial gradients in wave height and energy period were quantified using the difference between drifting Surface Wave Instrument Float with Tracking (SWIFT) measurements and the moored buoys, including a comparison of atlas values for these spatial gradients. In general, the atlas values agree well with the CDIP buoy data for significant wave height, but overestimate energy period and fail to capture wave direction trends. The atlas values overestimate observed power densities within a standard deviation of the observed values and capture observed variation in power density between different CDIP buoy locations. The atlas values underestimate observed spatial gradients for significant wave height and fail to capture observed spatial gradients for energy period. |
Arctic sea ice drift measured by shipboard marine radar Lund, B., H.C. Graber, P.O.G. Persson, M. Smith, M. Doble, J. Thomson, and P. Wadhams, "Arctic sea ice drift measured by shipboard marine radar," J. Geophys. Res., 123, 4298-4321, doi:10.1029/2018JC013769, 2018. |
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1 Jun 2018 |
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This study presents Arctic sea ice drift fields measured by shipboard marine X‐band radar (MR). The measurements are based on the maximum cross correlation between two sequential MR backscatter images separated ∼1 min in time, a method that is commonly used to estimate sea ice drift from satellite products. The advantage of MR is that images in close temporal proximity are readily available. A typical MR antenna rotation period is ∼12 s, whereas satellite revisit times can be on the order of days. The technique is applied to ∼4 weeks of measurements taken from R/V Sikuliaq in the Beaufort Sea in the fall of 2015. The resulting sea ice velocity fields have ∼500 m and up to ∼5 min resolution, covering a maximum range of ∼4 km. The MR velocity fields are validated using the GPS‐tracked motion of Surface Wave Instrument Float with Tracking (SWIFT) drifters, wave buoys, and R/V Sikuliaq during ice stations. The comparison between MR and reference sea ice drift measurements yields root‐mean‐square errors from 0.85.6 cm s-1. The MR sea ice velocity fields near the ice edge reveal strong horizontal gradients and peak speeds > 1 m s-1. The observed submesoscale sea ice drift processes include an eddy with ∼6 km diameter and vorticities < 2 (normalized by the Coriolis frequency) as well as converging and diverging flow with normalized divergences < 2 and > 1, respectively. The sea ice drift speed correlates only weakly with the wind speed (r2=0.34), which presents a challenge to conventional wisdom. |
Episodic reversal of autumn ice advance caused by release of ocean heat in the Beaufort Sea Smith, M., S. Stammerjohn, O. Persson, L. Rainville, G. Liu, W. Perrie, R. Robertson, J. Jackson, and J. Thomson, "Episodic reversal of autumn ice advance caused by release of ocean heat in the Beaufort Sea," J. Geophys. Res., 123, 3164-3185, doi:10.1002/2018JC013764, 2018. |
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1 May 2018 |
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High‐resolution measurements of the air‐ice‐ocean system during an October 2015 event in the Beaufort Sea demonstrate how stored ocean heat can be released to temporarily reverse seasonal ice advance. Strong on‐ice winds over a vast fetch caused mixing and release of heat from the upper ocean. This heat was sufficient to melt large areas of thin, newly formed pancake ice; an average of 10 MJ/m2 was lost from the upper ocean in the study area, resulting in ~35 cm pancake sea ice melt. Heat and salt budgets create a consistent picture of the evolving air‐ice‐ocean system during this event, in both a fixed and ice‐following (Lagrangian) reference frame. The heat lost from the upper ocean is large compared with prior observations of ocean heat flux under thick, multi‐year Arctic sea ice. In contrast to prior studies, where almost all heat lost goes into ice melt, a significant portion of the ocean heat released in this event goes directly to the atmosphere, while the remainder (~3040%) goes into melting sea ice. The magnitude of ocean mixing during this event may have been enhanced by large surface waves, reaching nearly 5 m at the peak, which are becoming increasingly common in the autumn Arctic Ocean. The wave effects are explored by comparing the air‐ice‐ocean evolution observed at short and long fetches, and a common scaling for Langmuir turbulence. After the event, the ocean mixed layer was deeper and cooler, and autumn ice formation resumed. |
Wave attenuation through an arctic marginal ice zone on 12 October 2015. 1. Measurement of wave spectra and ice features from Sentinel 1A Stopa, J.E., F. Ardhuin, J. Thomson, M.M. Smith, A. Kohout, M. Doble, and P. Wadhams, "Wave attenuation through an arctic marginal ice zone on 12 October 2015. 1. Measurement of wave spectra and ice features from Sentinel 1A," J. Geophys. Res., 123, 3619-3634, doi:10.1029/2018JC013791, 2018. |
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1 May 2018 |
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A storm with significant wave heights exceeding 4 m occurred in the Beaufort Sea on 1113 October 2015. The waves and ice were captured on 12 October by the Synthetic Aperture Radar (SAR) on board Sentinel‐1A, with Interferometric Wide swath images covering 400 x 1,100 km at 10 m resolution. This data set allows the estimation of wave spectra across the marginal ice zone (MIZ) every 5 km, over 400 km of sea ice. Since ice attenuates waves with wavelengths shorter than 50 m in a few kilometers, the longer waves are clearly imaged by SAR in sea ice. Obtaining wave spectra from the image requires a careful estimation of the blurring effect produced by unresolved wavelengths in the azimuthal direction. Using in situ wave buoy measurements as reference, we establish that this azimuth cutoff can be estimated in mixed ocean‐ice conditions. Wave spectra could not be estimated where ice features such as leads contribute to a large fraction of the radar backscatter variance. The resulting wave height map exhibits a steep decay in the first 100 km of ice, with a transition into a weaker decay further away. This unique wave decay pattern transitions where large‐scale ice features such as leads become visible. As in situ ice information is limited, it is not known whether the decay is caused by a difference in ice properties or a wave dissipation mechanism. The implications of the observed wave patterns are discussed in the context of other observations. |
Measurements of directional wave spectra and wind stress from a Wave Glider autonomous surface vehicle Thomson, J., J.B. Girton, R. Jha, and A. Trapani "Measurements of directional wave spectra and wind stress from a Wave Glider autonomous surface vehicle," J. Atmos. Ocean. Technol., 35, 347-363, doi:10.1175/JTECH-D-17-0091.1, 2018. |
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1 Feb 2018 |
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Methods for measuring waves and winds from a Wave Glider Autonomous Surface Vehicle (ASV) are described and evaluated. The wave method utilizes the frequency spectra of orbital velocities measured by GPS, and the wind stress method utilizes the frequency spectra of turbulent wind fluctuations measured by ultrasonic anemometer. Both methods evaluate contaminations from vehicle motion. The methods were evaluated with 68 days of data over a full range of open ocean conditions, in which wave heights varied from 1 to 8 m and wind speeds varied from 1 to 17 m/s. Reference data were collected using additional sensors onboard the vehicle. For the waves method, several additional datasets are included which use independently moored Datawell waverider buoys as reference data. Bulk wave parameters are determined waverider buoys as reference data. Bulk wave parameters are determined within 5% error, with biases of less than 5%. Wind stress is determined within 4% error, with 1% bias. Wave directional spectra also compare well, although the Wave Glider results have more spread at low frequencies. |
Turbulence from breaking surface waves at a river mouth Zippel, S.F., J. Thomson, and G. Farquharson, "Turbulence from breaking surface waves at a river mouth," J. Phys. Oceanogr., 48, 435-453, doi:10.1175/JPO-D-17-0122.1, 2018. |
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1 Feb 2018 |
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Observations of surface waves, currents, and turbulence at the Columbia River mouth are used to investigate the source and vertical structure of turbulence in the surface boundary layer. Turbulent velocity data collected on board freely drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys are corrected for platform motions to estimate turbulent kinetic energy (TKE) and TKE dissipation rates. Both of these quantities are correlated with wave steepness, which has previously been shown to determine wave breaking within the same dataset. Estimates of the turbulent length scale increase linearly with distance from the free surface, and roughness lengths estimated from velocity statistics scale with significant wave height. The vertical decay of turbulence is consistent with a balance between vertical diffusion and dissipation. Below a critical depth, a power-law scaling commonly applied in the literature works well to fit the data. Above this depth, an exponential scaling fits the data well. These results, which are in a surface-following reference frame, are reconciled with results from the literature in a fixed reference frame. A mapping between free-surface and mean-surface reference coordinates suggests 30% of the TKE is dissipated above the mean sea surface. |
Predicting deep water intrusions to Puget Sound, WA (USA), and the seasonal modulation of dissolved oxygen Deppe, R.W., J. Thomson, B. Polagye, and C. Krembs, "Predicting deep water intrusions to Puget Sound, WA (USA), and the seasonal modulation of dissolved oxygen," Estuar. Coasts, 41, 114-127, doi:10.1007/s12237-017-0274-6, 2017. |
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1 Jan 2018 |
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Observations and predictions regarding oceanic intrusions at the entrance to Puget Sound, WA (USA), are presented. Four years of seabed observations at Admiralty Inlet show episodic periods high salinity, coincident with landward residual currents near the seabed. The observed residual currents are consistent with an estuarine exchange flow during minimal tidal mixing, coincident with neap currents and maximum diurnal inequalities. These subtidal intrusions can carry dense water into Puget Sound and, thereby, renew the bottom water that is trapped landward of the sill. The oxygen concentration levels of these intrusions are often low, though not hypoxic, and may influence the oxygen levels in Puget Sound. The water mass properties of these intrusions are influenced strongly by regional dynamics, because the entrance to Puget Sound is connected to the open ocean via the Strait of Juan de Fuca. Coastal upwelling and discharge from the Fraser River discharge control the exchange flow in the Strait of Juan de Fuca and thus control the availability of dense water at the entrance to Puget Sound. The net effect of the tidal and regional dynamics is for intrusions with low oxygen levels to prevail in the late summer months. To predict intrusions in future years, an empirical method is developed and validated for daily application. The prediction method is based on publicly available operational data products and does not require in situ observations. In verification, 98% of intrusion events with dissolved oxygen less than 4.0 mg/L are successfully identified in a hindcast prediction for the 4-year observational record. |
Tidal energy resource characterization in Chacao Channel, Chile Guerra, M., R. Cienfuegos, J. Thomson, and L. Suarez, "Tidal energy resource characterization in Chacao Channel, Chile," Int. J. Mar. Energy, 20, doi:10.1016/j.ijome.2017.11.002, 2017. |
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1 Dec 2017 |
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Chacao Channel is an energetic tidal channel located at the northernmost part of the Chilean Patagonia. The channel has been previously identified as a prospective site for tidal energy extraction, however there has been only a limited understanding of the tidal flows. A new set of field measurements distributed along Chacao Channel is presented here for tidal energy resource characterization, including tidal elevations, tidal currents (in space and time), and turbulence. The field data also are used to calibrate and validate a FVCOM hydrodynamic numerical model of the entire channel, which is then used for tidal energy resource assessment. Field measurements indicate that tidal elevation range increases eastward along the channel, that tidal currents exceed 4 m s-1 at some points within the channel, and that turbulence intensity ranges between 5 and 20%. The data and numerical model results are used to estimate the kinetic power density of the tidal currents at Chacao Channel, which is in average 5 kW m-2. |
Calibrating a viscoelastic sea ice model for wave propagation in the Arctic fall marginal ice zone Cheng, S., W.E. Rogers, J. Thomson, M. Smith, M.J. Doble, P. Wadhams, A.L. Kohout, B. Lund, O.P.G. Persson, C.O. Collins III, S.F. Ackley, F. Montiel, and H.H. Shen, "Calibrating a viscoelastic sea ice model for wave propagation in the Arctic fall marginal ice zone," J. Geophys. Res., 122, 8770-8793, doi:10.1002/2017JC013275, 2017. |
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1 Nov 2017 |
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This paper presents a wave-in-ice model calibration study. Data used were collected in the thin ice of the advancing autumn marginal ice zone of the western Arctic Ocean in 2015, where pancake ice was found to be prevalent. Multiple buoys were deployed in seven wave experiments; data from four of these experiments are used in the present study. Wave attenuation coefficients are calculated utilizing wave energy decay between two buoys measuring simultaneously within the ice covered region. Wavenumbers are measured in one of these experiments. Forcing parameters are obtained from simultaneous in-situ and remote sensing observations, as well as forecast/hindcast models. Cases from three wave experiments are used to calibrate a viscoelastic model for wave attenuation/dispersion in ice cover. The calibration is done by minimizing the difference between modeled and measured complex wavenumber, using a multi-objective genetic algorithm. The calibrated results are validated using two methods. One is to directly apply the calibrated viscoelastic parameters to one of the wave experiments not used in the calibration and then compare the attenuation from the model with measured data. The other is to use the calibrated viscoelastic model in WAVEWATCH III over the entire western Beaufort Sea and then compare the wave spectra at two remote sites not used in the calibration. Both validations show reasonable agreement between the model and the measured data. The completed viscoelastic model is believed to be applicable to the fall marginal ice zone dominated by pancake ice. |
On the shape and likelihood of oceanic rogue waves Benetazzo, A., F. Ardhuin, F. Bergamasco, L. Cavaleri, P.V. Guimarães, M. Schwendeman, M. Sclavo, J. Thomson, and A. Torsello, "On the shape and likelihood of oceanic rogue waves," Sci. Reports, 7, doi:10.1038/s41598-017-07704-9, 2017. |
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15 Aug 2017 |
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We consider the observation and analysis of oceanic rogue waves collected within spatio-temporal (ST) records of 3D wave fields. This class of records, allowing a sea surface region to be retrieved, is appropriate for the observation of rogue waves, which come up as a random phenomenon that can occur at any time and location of the sea surface. To verify this aspect, we used three stereo wave imaging systems to gather ST records of the sea surface elevation, which were collected in different sea conditions. The wave with the ST maximum elevation (happening to be larger than the rogue threshold 1.25Hs) was then isolated within each record, along with its temporal profile. The rogue waves show similar profiles, in agreement with the theory of extreme wave groups. We analyze the rogue wave probability of occurrence, also in the context of ST extreme value distributions, and we conclude that rogue waves are more likely than previously reported; the key point is coming across them, in space as well as in time. The dependence of the rogue wave profile and likelihood on the sea state conditions is also investigated. Results may prove useful in predicting extreme wave occurrence probability and strength during oceanic storms. |
An autonomous approach to observing the seasonal ice zone in the western Arctic Lee, C.M., J. Thomson, and the Marginal Ice Zone and Arctic Sea State Teams, "An autonomous approach to observing the seasonal ice zone in the western Arctic," Oceanography, 30, 56-68, doi:10.5670/oceanog.2017.222, 2017. |
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1 Jun 2017 |
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The Marginal Ice Zone and Arctic Sea State programs examined the processes that govern evolution of the rapidly changing seasonal ice zone in the Beaufort Sea. Autonomous platforms operating from the ice and within the water column collected measurements across the atmosphere-ice-ocean system and provided the persistence to sample continuously through the springtime retreat and autumn advance of sea ice. Autonomous platforms also allowed operational modalities that reduced the field programs’ logistical requirements. Observations indicate that thermodynamics, especially the radiative balances of the ice-albedo feedback, govern the seasonal cycle of sea ice, with the role of surface waves confined to specific events. Continuous sampling from winter into autumn also reveals the imprint of winter ice conditions and fracturing on summertime floe size distribution. These programs demonstrate effective use of integrated systems of autonomous platforms for persistent, multiscale Arctic observing. Networks of autonomous systems are well suited to capturing the vast scales of variability inherent in the Arctic system. |
Sustained measurements of Southern Ocean airsea coupling from a Wave Glider autonomous surface vehicle Thomson, J., and J. Girton, "Sustained measurements of Southern Ocean airsea coupling from a Wave Glider autonomous surface vehicle," Oceanography, 30, 104-109, doi:10.5670/oceanog.2017.228, 2017. |
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1 Jun 2017 |
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The four-month mission of a Wave Glider in the Southern Ocean has demonstrated the capability for an autonomous surface vehicle to make sustained measurements of air-sea interactions in remote regions. Several new sensor payloads were integrated for this mission, including a three-axis sonic anemometer for turbulent wind stress estimation and a high-resolution atmospheric pressure gage. The mission focused on Drake Passage, where strong gradients are common along the Antarctic Circumpolar Current (ACC) fronts. Using satellite data products, pilots ashore were able to remotely navigate the Wave Glider across the ACC Polar Front and measure changes in air-sea coupling. The resulting data set combines the persistence of a mooring with the adaptability of a ship-based survey. |
Turbulence measurements from compliant moorings. Part I: Motion characterization Harding, S., L. Kilcher, and J. Thomson, "Turbulence measurements from compliant moorings. Part I: Motion characterization," J. Atmos. Ocean. Technol., 34, 1235-1247, doi:10.1175/JTECH-D-16-0189.1, 2017. |
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1 Jun 2017 |
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High-fidelity measurements of turbulence in the ocean have long been challenging to collect, in particular in the middle of the water column. In response, a measurement technique has been developed to deploy an acoustic Doppler velocimeter (ADV) to midwater locations on a compliant mooring. A variety of instrumentation platforms have been deployed as part of this work with a range of dynamic motion characteristics. The platforms discussed herein include the streamlined StableMoor buoy (SMB), the Tidal Turbulence Mooring (TTM) system based on a conventional 0.9-m spherical buoy, and a 100-lb sounding weight suspended from the stern of a research vessel. The ADV head motion is computed from inertial motion sensors integrated into an ADV, and the spectra of these signals are investigated to quantify the motion of each platform. The SMB with a single ADV head mounted on the nose provided the most stable platform for the measurement of tidal turbulence in the inertial subrange for flow speeds exceeding 1.0 m s1. The modification of the SMB with a transverse wing configuration for multiple ADVs showed a similar frequency response to the nose configuration in the horizontal plane but with large contamination in the vertical direction as a result of platform roll. While the ADV motion on the TTM was significant in the horizontal directions, the vertical motion of this configuration was the most stable of all configurations tested. The sounding weight measurements showed the greatest motion at the ADV head but are likely to be influenced by both prop-wash and vessel motion. |
Turbulence measurements from compliant moorings. Part II: Motion correction Kilcher, L.F., J. Thomson, S. Harding, and S. Nylund, "Turbulence measurements from compliant moorings. Part II: Motion correction," J. Atmos. Ocean. Technol., 34, 1249-1266, doi:10.1175/JTECH-D-16-0213.1, 2017. |
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1 Jun 2017 |
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Acoustic Doppler velocimeters (ADVs) are a valuable tool for making high-precision measurements of turbulence, and moorings are a convenient and ubiquitous platform for making many kinds of measurements in the ocean. However, because of concerns that mooring motion can contaminate turbulence measurements and that acoustic Doppler profilers make middepth velocity measurements relatively easy, ADVs are not frequently deployed from moorings. This work demonstrates that inertial motion measurements can be used to reduce motion contamination from moored ADV velocity measurements. Three distinct mooring platforms were deployed in a tidal channel with inertial-motion-sensor-equipped ADVs. In each case, motion correction based on the inertial measurements reduces mooring motion contamination of velocity measurements. The spectra from these measurements are consistent with other measurements in tidal channels and have an f-5/3slope at high frequencies consistent with Kolmogorov’s theory of isotropic turbulence. Motion correction also improves estimates of cross spectra and Reynolds stresses. A comparison of turbulence dissipation with flow speed and turbulence production indicates a bottom boundary layer productiondissipation balance during ebb and flood that is consistent with the strong tidal forcing at the site. These results indicate that inertial-motion-sensor-equipped ADVs are a valuable new tool for making high-precision turbulence measurements from moorings. |
Turbulence measurements from five-beam acoustic Doppler current profilers Guerra, M., and J. Thomson, "Turbulence measurements from five-beam acoustic Doppler current profilers," J. Atmos. Ocean. Technol., 34, 1267-1284, doi:10.1175/JTECH-D-16-0148.1, 2017. |
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1 Jun 2017 |
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Two new five-beam acoustic Doppler current profilers the Nortek Signature1000 AD2CP and the Teledyne RDI Sentinel V50 are demonstrated to measure turbulence at two energetic tidal channels within Puget Sound, Washington. The quality of the raw data is tested by analyzing the turbulent kinetic energy frequency spectra, the turbulence spatial structure function, the shear in the profiles, and the covariance Reynolds stresses. The five-beam configuration allows for a direct estimation of the Reynolds stresses from along-beam velocity fluctuations. The Nortek’s low Doppler noise and high sampling frequency allow for the observation of the turbulent inertial subrange in both the frequency spectra and the turbulence structure function. The turbulence parameters obtained from the five-beam acoustic Doppler current profilers are validated with turbulence data from simultaneous measurements with acoustic Doppler velocimeters. These combined results are then used to assess a turbulent kinetic energy budget in which depth profiles of the turbulent kinetic energy dissipation and production rates are compared. The associated codes are publicly available on the MATLAB File Exchange website. |
Tidal energy resource measurements Thomson, J., B. Polagye, and V.S. Neary, "Tidal energy resource measurements," in Marine Renewable Energy, Z. Yang and A. Copping, eds., 121-136, doi:10.1007/978-3-319-53536-4_5 (Springer, 2017). |
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17 May 2017 |
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When conducting tidal energy resource characterization and assessment, it is important to capture the strong variations of tidal currents in time and space. Field measurements can quantify many of these variations, which have both deterministic and stochastic components. The deterministic components occur on timescales of hours to years. As such, they are repeatable and well-suited to harmonic analyses associated with astronomical tidal forcing. The stochastic components are well-suited to statistical descriptions of fluid turbulence , from the short scales (milliseconds and millimeters), where dissipation occurs, to the long scales (seconds and meters), where large eddies occur. While the resolution of deterministic components may be adequate for characterizing annual energy production, both components need to be quantified to determine design loads on tidal energy conversion devices. In addition to the direct utility of field measurements to characterize and assess the tidal energy resource, field measurements are also essential to validate computational models used to assess the resource over large spatial domains. |
Surface wave breaking over sheared currents: Observations from the mouth of the Columbia River Zipple, S., and J. Thomson, "Surface wave breaking over sheared currents: Observations from the mouth of the Columbia River," J. Geophys. Res., 122, 3311-3328, doi:10.1002/2016JC012498, 2017. |
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26 Apr 2017 |
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SWIFT website Measurements of waves and currents from freely drifting buoys are used to evaluate wave breaking parameterizations at the Mouth of the Columbia River, where breaking occurs in intermediate depths and in the presence of vertically sheared currents. Breaking waves are identified using images collected with cameras onboard the buoys, and the breaking activity is well-correlated with wave steepness. Vertical shear in the currents produces a frequency-dependent effective current that modifies the linear dispersion relation. Accounting for these sheared currents in the wavenumber spectrum is essential in calculating the correct wave steepness; without this, wave steepness can be over (under) estimated on opposing (following) currents by up to 20%. The observed bulk steepness values suggest a limiting value of 0.4. The observed fraction of breaking waves is in good agreement with several existing models, each based on wave steepness. Further, a semispectral model designed for all depth regimes also compares favorably with measured breaking fractions. In this model, the majority of wave breaking is predicted to occur in the higher frequency bands (i.e., short waves). There is a residual dependence on directional spreading, in which wave breaking decreases with increasing directional spread. |
Sharp-crested breaking surface waves observed from a ship-based stereo video system Schwendeman, M.S., and J. Thomson, "Sharp-crested breaking surface waves observed from a ship-based stereo video system," J. Phys. Oceanogr., 47, 775-792, doi:10.1175/JPO-D-16-0187.1, 2017. |
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1 Apr 2017 |
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Supporting data: UW Research Works Archive A new ship-based stereo video system is used to observe breaking ocean waves (i.e., whitecaps) as three-dimensional surfaces evolving in time. First, the stereo video measurements of all waves (breaking and nonbreaking) are shown to compare well with statistical parameters from traditional buoy measurements. Next, the breaking waves are detected based on the presence of whitecap foam, and the geometry of these waves is investigated. The stereo measurements show that the whitecaps are characterized by local extremes of surface slope, though the larger-scale, crest-to-trough steepness of these waves is unremarkable. Examination of 103 breaking wave profiles further demonstrates the pronounced increase in the local wave steepness near the breaking crest, as estimated using a Hilbert transform. These crests are found to closely resemble the sharp corner of the theoretical Stokes limiting wave. Results suggest that nonlinear wave group dynamics are a key mechanism for breaking, as the phase speed of the breaking waves is slower than predicted by the linear dispersion relation. The highly localized and transient steepness, along with the deviation from linear phase speed, explains the inability of conventional wave buoys to observe the detailed geometry of breaking waves. |
Observations of the shape and group dynamics of rogue waves Gemmrich, J., and J. Thomson, "Observations of the shape and group dynamics of rogue waves," Geophys. Res. Lett., 44, doi:10.1002/2016GL072398. |
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17 Feb 2017 |
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Surface elevation records from two locations in the northeast Pacific are used to examine rogue waves and the relationship to wave groups. Three hundred individual rogue waves with heights greater than 2.2 times the significant wave height are found in analyzing >2 × 106 wave groups. In contrast to recent nonlinear modeling results, we do not find that rogue waves occur at the front of wave groups. There is a tendency for steep waves to occur at the front of a group, but these are not the largest waves of the group and do not meet the rogue wave criterion. Rogue waves are most commonly located in the center of the group, but their height ratio to the neighboring crest is greater than in the average wave group. Assessing group dynamics in terms of spectral width suggests that random superposition of nonlinear waves is sufficient to explain the observations of individual rogue waves. |
Doppler correction of wave frequency-spectra measured by underway vessels Collins, C.O., B. Blomquist, O. Persson, B. Lund, W.E. Rogers, J. Thomson, D. Wang, M. Smith, M. Doble, P. Wadhams, A. Kohout, C. Fairall, and H.C. Graber, "Doppler correction of wave frequency-spectra measured by underway vessels," J. Atmos. Ocean. Technol., 34, 429–436, doi:10.1175/JTECH-D-16-0138.1, 2017. |
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1 Feb 2017 |
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"Sea State and Boundary Layer Physics in the Emerging Arctic Ocean" is an ongoing Departmental Research Initiative sponsored by the Office of Naval Research. The field component took place in the fall of 2015 within the Beaufort and Chukchi Seas and involved the deployment of a number of wave instruments including a downward looking Riegl laser rangefinder mounted on the foremast of the R/V Sikuliaq. Although time series measurements on a stationary vessel are thought to be accurate, an underway vessel introduces a Doppler shift to the observed wave spectrum. This Doppler shift is a function of the wavenumber vector and the velocity vector of the vessel. Of all the possible relative angles between wave direction and vessel heading there are two main scenarios: I) vessel steaming into waves and II) vessel steaming with waves. Previous studies have considered only a subset of cases, and all were in scenario I. This was likely to avoid ambiguities, which arise when the vessel is steaming with waves. This study addresses the ambiguities and analyzes arbitrary cases. In addition, a practical method is provided which is useful in situations when the vessel is changing speed or heading. These methods improved the laser rangefinder estimates of spectral shapes and peak parameters when compared to nearby buoys and a spectral wave model. |
Measuring ocean waves in sea ice using SAR imagery: A quasi-deterministic approach evaluated with Sentinel-1 and in situ data Ardhuin, F., J. Stopa, B. Chapron, F. Collard, M. Smith, J. Thomson, M. Doble, B. Blomquist, O. Persson, C.O. Collins III, and P. Wadhams, "Measuring ocean waves in sea ice using SAR imagery: A quasi-deterministic approach evaluated with Sentinel-1 and in situ data," Remote Sens. Environ., 189, 211-222, doi:10.1016/j.rse.2016.11.024, 2017. |
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1 Feb 2017 |
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Dissipation of wind waves by pancake and frazil ice in the autumn Beaufort Sea Rogers, W.E., J. Thomson, H.H. Shen, M.J. Doble, P. Wadhams, and S. Cheng, "Dissipation of wind waves by pancake and frazil ice in the autumn Beaufort Sea," J. Geophys. Res., 121, 7991-8007, doi:10.1002/2016JC012251, 2016. |
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1 Nov 2016 |
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A model for wind-generated surface gravity waves, WAVEWATCH III®, is used to analyze and interpret buoy measurements of wave spectra. The model is applied to a hindcast of a wave event in sea ice in the western Arctic, October 1114 2015, for which extensive buoy and ship-borne measurements were made during a research cruise. The model, which uses a viscoelastic parameterization to represent the impact of sea ice on the waves, is found to have good skill after calibration of the effective viscosity for prediction of total energy, but over-predicts dissipation of high frequency energy by the sea ice. This shortcoming motivates detailed analysis of the apparent dissipation rate. A new inversion method is applied to yield, for each buoy spectrum, the inferred dissipation rate as a function of wave frequency. For 102 of the measured wave spectra, visual observations of the sea ice were available from buoy-mounted cameras, and ice categories (primarily for varying forms of pancake and frazil ice) are assigned to each based on the photographs. When comparing the inversion-derived dissipation profiles against the independently derived ice categories, there is remarkable correspondence, with clear sorting of dissipation profiles into groups of similar ice type. These profiles are largely monotonic: they do not exhibit the "roll-over" that has been found at high frequencies in some previous observational studies. This article is protected by copyright. All rights reserved. |
Inner Shelf Dynamics Science and Experiment Plan Feddersen, F., et al., "Inner Shelf Dynamics Science and Experiment Plan," APL-UW TR 1602, Technical Report, Applied Physics Laboratory, University of Washington, Seattle, October 2016, 35pp. |
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31 Oct 2016 |
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The deep ocean, continental shelf, and surf zone are defined by their unique physical processes and dynamics. The nearshore region from about 50 m water depth to the outer edge of the surf zone (SZ) is known as the inner shelf. This region is characterized by overlapping and interacting surface and bottom boundary layers. At the offshore side of the inner shelf, instabilities from wind-driven currents and fronts create cross-shelf meanders and eddies. In addition, energetic nonlinear internal waves (NLIWs) are ubiquitous on the inner shelf. |
Stratified Ocean Dynamics in the Arctic: Science and Experiment Plan Lee, C.M., et al., "Stratified Ocean Dynamics in the Arctic: Science and Experiment Plan," APL-UW TR 1601, Technical Report, Applied Physics Laboratory, University of Washington, Seattle, September 2016, 46pp. |
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15 Sep 2016 |
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Vertical and lateral water properties and density structure within the Arctic Ocean are intimately related to the ocean circulation, and have profound consequences for sea ice growth and retreat as well as for propagation of acoustic energy at all scales. Our current understanding of the dynamics governing arctic upper ocean stratification and circulation derives largely from a period when extensive ice cover modulated the oceanic response to atmospheric forcing. Recently, however, there has been significant arctic warming, accompanied by changes in the extent, thickness distribution, and properties of the arctic sea ice cover. The need to understand these changes and their impact on arctic stratification and circulation, sea ice evolution, and the acoustic environment motivate the Office of Naval Research (ONR) Stratified Ocean Dynamics of the Arctic Departmental Research Initiative. |
Emerging trends in the sea state of the Beaufort and Chukchi seas Thomson, J., et al., "Emerging trends in the sea state of the Beaufort and Chukchi seas," Ocean Modell., 105, doi:10.1016/j.ocemod.2016.02.009, 2016. |
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1 Sep 2016 |
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The sea state of the Beaufort and Chukchi seas is controlled by the wind forcing and the amount of ice-free water available to generate surface waves. Clear trends in the annual duration of the open water season and in the extent of the seasonal sea ice minimum suggest that the sea state should be increasing, independent of changes in the wind forcing. Wave model hindcasts from four selected years spanning recent conditions are consistent with this expectation. In particular, larger waves are more common in years with less summer sea ice and/or a longer open water season, and peak wave periods are generally longer. The increase in wave energy may affect both the coastal zones and the remaining summer ice pack, as well as delay the autumn ice-edge advance. However, trends in the amount of wave energy impinging on the ice-edge are inconclusive, and the associated processes, especially in the autumn period of new ice formation, have yet to be well-described by in situ observations. There is an implicit trend and evidence for increasing wave energy along the coast of northern Alaska, and this coastal signal is corroborated by satellite altimeter estimates of wave energy. |
Spatial characteristics of ocean surface waves Gemmrich, J., J. Thomson, W.E. Rogers, A. Pleskachevsky, and S. Lehner, "Spatial characteristics of ocean surface waves," Ocean Dyn., 66, 1025-1035, doi:10.1007/s10236-016-0967-6, 2016. |
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1 Aug 2016 |
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The spatial variability of open ocean wave fields on scales of O (10 km) is assessed from four different data sources: TerraSAR-X SAR imagery, four drifting SWIFT buoys, a moored waverider buoy, and WAVEWATCH III® model runs. Two examples from the open north-east Pacific, comprising of a pure wind sea and a mixed sea with swell, are given. Wave parameters attained from observations have a natural variability, which decreases with increasing record length or acquisition area. The retrieval of dominant wave scales from point observations and model output are inherently different to dominant scales retrieved from spatial observations. This can lead to significant differences in the dominant steepness associated with a given wave field. These uncertainties have to be taken into account when models are assessed against observations or when new wave retrieval algorithms from spatial or temporal data are tested. However, there is evidence of abrupt changes in wave field characteristics that are larger than the expected methodological uncertainties. |
On the modeling of wave-enhanced turbulence nearshore Moghimi, S., J. Thomson, T. Özkan-Haller, L. Umlauf, and S. Zippel, "On the modeling of wave-enhanced turbulence nearshore," Ocean Modell., 103, 118-132, doi:10.1016/j.ocemod.2015.11.004, 2016. |
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1 Jul 2016 |
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A high resolution k ω two-equation turbulence closure model, including surface wave forcing was employed to fully resolve turbulence dissipation rate profiles close to the ocean surface. Model results were compared with observations from Surface Wave Instrument Floats with Tracking (SWIFTs) in the nearshore region at New River Inlet, North Carolina USA, in June 2012. A sensitivity analysis for different physical parameters and wave and turbulence formulations was performed. The flux of turbulent kinetic energy (TKE) prescribed by wave dissipation from a numerical wave model was compared with the conventional prescription using the wind friction velocity. A surface roughness length of 0.6 times the significant wave height was proposed, and the flux of TKE was applied at a distance below the mean sea surface that is half of this roughness length. The wave enhanced layer had a total depth that is almost three times the significant wave height. In this layer the non-dimensionalized Terray scaling with power of 1.8 (instead of 2) was applicable. |
Wave breaking turbulence in the ocean surface layer Thomson, J., M.S. Schwendeman, S.F. Zippel, S. Moghimi, J. Gemmrich, and W.E. Rogers, "Wave breaking turbulence in the ocean surface layer," J. Phys. Oceanogr., 46, 1857-1870, doi:10.1175/JPO-D-15-0130.1, 2016. |
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1 Jun 2016 |
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Observations of winds, waves, and turbulence at the ocean surface are compared with several analytic formulations and a numerical model for the input of turbulent kinetic energy by wave breaking and the subsequent dissipation. The observations are generally consistent with all of the formulations, although some differences are notable at winds greater than 15 m/s. The depth dependence of the turbulent dissipation rate beneath the waves is fit to a decay scale, which is sensitive to the choice of vertical reference frame. In the surface following reference frame, the strongest turbulence is isolated within a shallow region of depths much less than one significant wave height. In a fixed reference frame, the strong turbulence penetrates to depths that are at least half of the significant wave height. This occurs because the turbulence of individual breakers persists longer that the dominant period of the waves, and thus the strong surface turbulence is carried from crest to trough with the wave orbital motion. |
Scaling observations of surface waves in the Beaufort Sea Smith, M., and J. Thomson, "Scaling observations of surface waves in the Beaufort Sea," Elem. Sci. Anth., 4, 000097, doi:10.12952/journal.elementa.000097, 2016. |
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14 Apr 2016 |
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The rapidly changing Arctic sea ice cover affects surface wave growth across all scales. Here, in situ measurements of waves, observed from freely-drifting buoys during the 2014 open water season, are interpreted using open water distances determined from satellite ice products and wind forcing time series measured in situ with the buoys. A significant portion of the wave observations were found to be limited by open water distance (fetch) when the wind duration was sufficient for the conditions to be considered stationary. The scaling of wave energy and frequency with open water distance demonstrated the indirect effects of ice cover on regional wave evolution. Waves in partial ice cover could be similarly categorized as distance-limited by applying the same open water scaling to determine an ‘effective fetch’. The process of local wave generation in ice appeared to be a strong function of the ice concentration, wherein the ice cover severely reduces the effective fetch. The wave field in the Beaufort Sea is thus a function of the sea ice both locally, where wave growth primarily occurs in the open water between floes, and regionally, where the ice edge may provide a more classic fetch limitation. Observations of waves in recent years may be indicative of an emerging trend in the Arctic Ocean, where we will observe increasing wave energy with decreasing sea ice extent. |
Airsea interactions in the marginal ice zone Zippel, S., and J. Thomson, "Airsea interactions in the marginal ice zone," Elem. Sci. Anth., 4, 000095, doi:10.12952/journal.elementa.000095, 2016. |
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31 Mar 2016 |
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The importance of waves in the Arctic Ocean has increased with the significant retreat of the seasonal sea-ice extent. Here, we use wind, wave, turbulence, and ice measurements to evaluate the response of the ocean surface to a given wind stress within the marginal ice zone, with a focus on the local wind input to waves and subsequent ocean surface turbulence. Observations are from the Beaufort Sea in the summer and early fall of 2014, with fractional ice cover of up to 50%. Observations showed strong damping and scattering of short waves, which, in turn, decreased the wind energy input to waves. Near-surface turbulent dissipation rates were also greatly reduced in partial ice cover. The reductions in waves and turbulence were balanced, suggesting that a wind-wave equilibrium is maintained in the marginal ice zone, though at levels much less than in open water. These results suggest that air-sea interactions are suppressed in the marginal ice zone relative to open ocean conditions at a given wind forcing, and this suppression may act as a feedback mechanism in expanding a persistent marginal ice zone throughout the Arctic. |
Wind and wave influences on sea ice floe size and leads in the Beaufort and Chukchi seas during the summer-fall transition 2014 Wang, Y., B. Holt, W.E. Rogers, J. Thomson, and H.H. Shen, "Wind and wave influences on sea ice floe size and leads in the Beaufort and Chukchi seas during the summer-fall transition 2014," J. Geophys. Res., 121, 1502-1525, doi:10.1002/2015JC011349, 2016. |
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20 Feb 2016 |
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Sea ice floe size distribution and lead properties in the Beaufort and Chukchi Seas are studied in the summer-fall transition 2014 to examine the impact on the sea ice cover from storms and surface waves. Floe size distributions are analyzed from MEDEA, Landsat8, and RADARSAT-2 imagery, with a resolution span of 1100 m. Landsat8 imagery is also used to identify the orientation and spacing of leads. The study period centers around three large wave events during AugustSeptember 2014 identified by SWIFT buoys and WAVEWATCH III model data. The range of floe sizes from different resolutions provides the overall distribution across a wide range of ice properties and estimated thickness. All cumulative floe size distribution curves show a gradual bending toward shallower slopes for smaller floe sizes. The overall slopes in the cumulative floe size distribution curves from Landsat8 images are lower than, while those from RADARSAT-2 are similar to, previously reported results in the same region and seasonal period. The MEDEA floe size distributions appeared to be sensitive to the passage of storms. Lead orientations, regardless of length, correlate slightly better with the peak wave direction than with the mean wave direction. Their correlation with the geostrophic wind is stronger than with the surface wind. The spacing between shorter leads correlates well with the local incoming surface wavelengths, obtained from the model peak wave frequency. The information derived shows promise for a coordinated multisensor study of storm effects in the Arctic marginal ice zone. |
Observations of whitecap coverage and the relation to wind stress, wave slope, and turbulent dissipation Schwendeman, M., and J. Thomson, "Observations of whitecap coverage and the relation to wind stress, wave slope, and turbulent dissipation," J. Geophys. Res., 120, 8346-8363, doi:10.1002/2015JC011196, 2015. |
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28 Dec 2015 |
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Shipboard measurements of whitecap coverage are presented from two cruises in the North Pacific, and compared with in situ measurements of wind speed and friction velocity, average wave steepness, and near-surface turbulent dissipation. A threshold power law fit is proposed for all variables, which incorporates the flexibility of a power law with the threshold behavior commonly seen in whitecapping. The fit of whitecap coverage to wind speed, U10, closely matches similar relations from three recent studies, particularly in the range of 614 m/s. At higher wind speeds, the whitecap coverage data level off relative to the fits, and an analysis of the residuals shows some evidence of reduced whitecapping in rapidly developing waves. Wave slope variables are examined for potential improvement over wind speed parameterizations. Of these variables, the mean square slope of the equilibrium range waves has the best statistics, which are further improved after normalizing by the directional spread and frequency bandwidth. Finally, the whitecap coverage is compared to measurements of turbulent dissipation. Though still statistically significant, the correlation is worse than the wind or wave relations, and residuals show a strong negative trend with wave age. This may be due to an increased influence of microbreaking in older wind seas. |
Observations of whitecap coverage and the relation to wind stress, wave slope, and turbulent dissipation Schwendeman, M., and J. Thomson, "Observations of whitecap coverage and the relation to wind stress, wave slope, and turbulent dissipation," J. Geophys. Res., 120, 8346-8363, doi:10.1002/2015JC011196, 2015. |
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28 Dec 2015 |
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Shipboard measurements of whitecap coverage are presented from two cruises in the North Pacific, and compared with in situ measurements of wind speed and friction velocity, average wave steepness, and near-surface turbulent dissipation. A threshold power law fit is proposed for all variables, which incorporates the flexibility of a power law with the threshold behavior commonly seen in whitecapping. The fit of whitecap coverage to wind speed, U10, closely matches similar relations from three recent studies, particularly in the range of 614 m/s. At higher wind speeds, the whitecap coverage data level off relative to the fits, and an analysis of the residuals shows some evidence of reduced whitecapping in rapidly developing waves. Wave slope variables are examined for potential improvement over wind speed parameterizations. Of these variables, the mean square slope of the equilibrium range waves has the best statistics, which are further improved after normalizing by the directional spread and frequency bandwidth. Finally, the whitecap coverage is compared to measurements of turbulent dissipation. Though still statistically significant, the correlation is worse than the wind or wave relations, and residuals show a strong negative trend with wave age. This may be due to an increased influence of microbreaking in older wind seas. |
Biofouling effects on the response of a wave measurement buoy in deep water Thomson, J., J. Talbert, A. de Klerk, A. Brown, M. Schwendeman, J. Goldsmith, J. Thomas, C. Olfe, G. Cameron, and C. Meinig, "Biofouling effects on the response of a wave measurement buoy in deep water," J. Atmos. Ocean. Technol., 32, 1281-1286, doi:10.1175/JTECH-D-15-0029.1, 2015. |
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1 Jun 2015 |
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The effects of biofouling on a wave measurement buoy are examined using concurrent data collected with two Datawell Waveriders at Ocean Station P: one heavily biofouled at the end of a 26-month deployment, the other newly deployed and clean. The effects are limited to the high-frequency response of the buoy and are correctly diagnosed with the spectral "check factors" that compare horizontal and vertical displacements. A simple prediction for the progressive change in frequency response during biofouling reproduces the check factors over time. The bulk statistical parameters of significant wave height, peak period, average period, and peak direction are only slightly affected by the biofouling because the contaminated frequencies have very low energy throughout the comparison dataset. |
Estimating wave energy dissipation in the surf zone using thermal infrared imagery Carini, R.J. C.C. Chickadel, A.T. Jessup, and J. Thomson, "Estimating wave energy dissipation in the surf zone using thermal infrared imagery," J. Geophys. Res., 120, 3937-3957, doi:10.1002/2014JC010561, 2015. |
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1 Jun 2015 |
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Thermal infrared (IR) imagery is used to quantify the high spatial and temporal variability of dissipation due to wave breaking in the surf zone. The foam produced in an actively breaking crest, or wave roller, has a distinct signature in IR imagery. A retrieval algorithm is developed to detect breaking waves and extract wave roller length using measurements taken during the Surf Zone Optics 2010 experiment at Duck, NC. The remotely derived roller length and an in situ estimate of wave slope are used to estimate dissipation due to wave breaking by means of the wave-resolving model by Duncan (1981). The wave energy dissipation rate estimates show a pattern of increased breaking during low tide over a sand bar, consistent with in situ turbulent kinetic energy dissipation rate estimates from fixed and drifting instruments over the bar. When integrated over the surf zone width, these dissipation rate estimates account for 4069% of the incoming wave energy flux. The Duncan (1981) estimates agree with those from a dissipation parameterization by Janssen and Battjes (2007), a wave energy dissipation model commonly applied within nearshore circulation models. |
Characterization of turbulence anisotropy, coherence, and intermittency at a prospective tidal energy site: Observational data analysis McCaffrey, K., B. Fox-Kemper, P.E. Hamlington, and J. Thomson, "Characterization of turbulence anisotropy, coherence, and intermittency at a prospective tidal energy site: Observational data analysis," Renewable Energy, 76, 441-453, doi:10.1016/j.renene.2014.11.063, 2015. |
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1 Apr 2015 |
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As interest in marine renewable energy increases, observations are crucial for understanding the environments that prospective turbines will encounter. Data from an acoustic Doppler velocimeter in Puget Sound, WA are used to perform a detailed characterization of the turbulent flow encountered by a turbine in a tidal strait. Metrics such as turbulence intensity, structure functions, probability density functions, intermittency, coherent turbulence kinetic energy, anisotropy invariants, and a new scalar measure of anisotropy are used to characterize the turbulence. The results indicate that the scalar anisotropy magnitude can be used to identify and parameterize coherent, turbulent events in the flow. An analysis of the anisotropy characteristics leads to a physical description of turbulent stresses as being primarily one- or two-dimensional, in contrast to isotropic, three-dimensional turbulence. A new measure of the anisotropy magnitude is introduced to quantify the level of anisotropic, coherent turbulence in a coordinate-independent way. These diagnostics and results will be useful for improved realism in modeling the performance and loading of turbines in realistic ocean environments. |
Turbulence measurements from moving platforms Thomson, J., J. Talbert, A. de Klerk, S. Zippel, M. Guerra, and L. Kilcher, "Turbulence measurements from moving platforms," Proc. 11th IEEE/OES Current, Waves and Turbulence Measurement (CWTM) Workshop, 2-6 March, St. Petersburg, FL, doi:10.1109/CWTM.2015.7098107 (IEEE, 2015). |
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2 Mar 2015 |
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Two recent methods for making high-fidelity turbulence measurements from moving platforms are described and demonstrated. The first is a method for measuring profiles of near-surface turbulence from a wave-following 'SWIFT' buoy. The second is a method for measuring time series of turbulence from a submerged compliant mooring. Both approaches use coherent Doppler instruments and inertial motion units (IMUs). In the buoy method, wave motions (e.g., pitch, roll, and heave) are quantified via GPS and IMU measurements. These wave motions are not present in the turbulence observations, because buoy follows the wave orbital motion, and thus the turbulent velocities are processed in the wave-following reference frame. In the mooring method, IMU measurements track the mooring motions (e.g., strum and kiting) and these motions are removed in post-processing to obtain turbulent velocities in the fixed earth reference frame. These approaches successfully quantify turbulence in regions previously unavailable or limited by the noise and spatial aliasing of sampling from bottom-mounted platforms. |
Wave breaking and turbulence at a tidal inlet Zippel, S., and J. Thomson, "Wave breaking and turbulence at a tidal inlet," J. Geophys. Res., 120, 1016-1031, doi:10.1002/2014JC010025, 2015. |
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1 Feb 2015 |
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Field measurements collected with surface drifters at New River Inlet (NC, USA) are used to characterize wave breaking and turbulence in the presence of currents. Shoreward wave evolution is affected by currents, and breaking is observed in deeper water with opposing currents (ebb tides) relative to the following currents (flood tides). Wave dissipation models are evaluated with observed cross-shore gradients in wave energy flux. Wave dissipation models that include the effects of currents are better correlated with the observations than the depth-only models. Turbulent dissipation rates measured in the breaking regions are used to evaluate two existing scaling models for the vertical structure and magnitude of turbulent dissipation relative to wave dissipation. Although both describe the rapid decay of turbulence beneath the surface, exponential vertical scaling by water depth is superior to power law vertical scaling by wave height. |
A horizon-tracking method for shipboard video stabilization and rectification Schwendeman, M., and J. Thomson, "A horizon-tracking method for shipboard video stabilization and rectification," J. Atmos. Ocean. Technol., 32, 164-176, doi:10.1175/JTECH-D-14-00047.1, 2015. |
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1 Jan 2015 |
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An algorithm is presented for the stabilization and rectification of digital video from floating platforms. The method relies on a horizon-tracking technique that was tested under a variety of lighting and sea-state conditions for 48 h of video data over 12 days during a research cruise in the North Pacific Ocean. In this dataset, the horizon was correctly labeled in 92% of the frames in which it was present. The idealized camera model assumes pure pitch-and-roll motion, a flat sea surface, and an unobstructed horizon line. Pitch and roll are defined along the camera look direction rather than in traditional ship coordinates, such that the method can be used for any heading relative to the ship. The uncertainty in pitch and roll is estimated from the uncertainties of the horizon-finding method. These errors are found to be of the order 0.6° in roll and 0.3° in pitch. Errors in rectification are shown to be dominated by the uncertainty in camera height, which may change with the heave motion of a floating platform. The propagation of these errors is demonstrated for the breaking-wave distribution Λ(c). A toolbox for implementation of this method in MATLAB is shared via the MATLAB File Exchange. |
Wave breaking turbulence at the offshore front of the Columbia River Plume Thomson, J., A.R. Horner-Devine, S. Zippel, C. Rusch, and W. Geyer, "Wave breaking turbulence at the offshore front of the Columbia River Plume," Geophys. Res. Lett., 41, 8987-8993, doi:10.1002/2014GL062274, 2014. |
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28 Dec 2014 |
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Observations at the Columbia River plume show that wave breaking is an important source of turbulence at the offshore front, which may contribute to plume mixing. The lateral gradient of current associated with the plume front is sufficient to block (and break) shorter waves. The intense whitecapping that then occurs at the front is a significant source of turbulence, which diffuses downward from the surface according to a scaling determined by the wave height and the gradient of wave energy flux. This process is distinct from the shear-driven mixing that occurs at the interface of river water and ocean water. Observations with and without short waves are examined, especially in two cases in which the background conditions (i.e., tidal flows and river discharge) are otherwise identical. |
Historical Wave and Wind Observations at Ocean Station P Belka, D.J., M. Schwendeman, J. Thomson, and M.F. Cronin, "Historical Wave and Wind Observations at Ocean Station P," Technical Report, APL-UW TR 1407, Applied Physics Laboratory, University of Washington, Seattle, August 2014, 15 pp. |
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1 Aug 2014 |
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An historical data set with 30 years of wave and wind observations from Ocean Weather Station P (50°N, 145°W) is described and validated against modern measurements. Observation biases are discussed and corrections are made where appropriate. Climate trends are explored, including a negative correlation between waves and the Pacific Decadal Oscillation. The validated historical data are deposited in a public archive with online access. |
Video recognition of breaking waves Rusch, C., J. Thomson, S. Zippel, and M. Schwendeman, "Video recognition of breaking waves," Proc., OCEANS'14, 14-19 September, St. John's, Newfoundland (MTS/IEEE, 2014). |
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15 Jul 2014 |
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An algorithm is presented to automate the identification of breaking waves in images collected with a camera on a drifting buoy. Each image is given a score from four separate analysis techniques: brightness detection, pixel histogram, entropy (texture) analysis, and glare identification. By combining these in a composite score, potential breaking wave images are detected and the number of images requiring manual review is a small fraction of the original set. Most of the images with false breaking wave signals due to sun glare are identified and removed. The final output is the wave-breaking rate over the length of the video capture. |
Noise correction of turbulent spectra obtained from acoustic Doppler velocimeters Durgesh, V., J. Thomson, M. Richmond, and B. Polagye, "Noise correction of turbulent spectra obtained from acoustic Doppler velocimeters," Flow Meas. Instrum., 37, 29-41, doi:10.1016/j.flowmeasinst.2014.03.001, 2014. |
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1 Jun 2014 |
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Velocity spectra are essential in characterizing turbulent flows. The Acoustic Doppler Velocimeter (ADV) provides three-dimensional time series data at a single point in space which are used for calculating velocity spectra. However, ADV data are susceptible to contamination from various sources, including instrument noise, which is the intrinsic limit to the accuracy of acoustic Doppler processing. This contamination results in a flattening of the velocity spectra at high frequencies (O(10)Hz). |
Swell and sea in the emerging Arctic Ocean Thomson, J., and W.E. Rogers, "Swell and sea in the emerging Arctic Ocean," Geophys. Res. Lett., 41, 3136-3140, doi:10.1002/2014GL059983, 2014. |
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16 May 2014 |
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Ocean surface waves (sea and swell) are generated by winds blowing over a distance (fetch) for a duration of time. In the Arctic Ocean, fetch varies seasonally from essentially zero in winter to hundreds of kilometers in recent summers. Using in situ observations of waves in the central Beaufort Sea, combined with a numerical wave model and satellite sea ice observations, we show that wave energy scales with fetch throughout the seasonal ice cycle. Furthermore, we show that the increased open water of 2012 allowed waves to develop beyond pure wind seas and evolve into swells. The swells remain tied to the available fetch, however, because fetch is a proxy for the basin size in which the wave evolution occurs. Thus, both sea and swell depend on the open water fetch in the Arctic, because the swell is regionally driven. This suggests that further reductions in seasonal ice cover in the future will result in larger waves, which in turn provide a mechanism to break up sea ice and accelerate ice retreat. |
Flow-noise and turbulence in two tidal channels Bassett, C., J. Thomson, P. H. Dahl, and B. Polagye, "Flow-noise and turbulence in two tidal channels," J. Acoust. Soc. Am., 135(4), 1764-1774, doi:10.1121/1.4867360, 2014. |
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13 May 2014 |
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Flow-noise resulting from oceanic turbulence and interactions with pressure-sensitive transducers can interfere with ambient noise measurements. This noise source is particularly important in low-frequency measurements (f < 100 Hz) and in highly turbulent environments such as tidal channels. This work presents measurements made in the Chacao Channel, Chile, and in Admiralty Inlet, Puget Sound, WA. In both environments, peak currents exceed 3 m/s and pressure spectral densities attributed to flow-noise are observed at frequencies up to 500 Hz. At 20 Hz, flow-noise exceeds mean slack noise levels by more than 50 dB. Two semi-empirical flow-noise models are developed and applied to predict flow-noise at frequencies from 20 to 500 Hz using measurements of current velocity and turbulence. The first model directly applies mean velocity and turbulence spectra while the second model relies on scaling arguments that relate turbulent dissipation to the mean velocity. Both models, based on prior formulations for infrasonic (f < 20 Hz) flow-noise, agree well with observations in Chacao Channel. In Admiralty Inlet, good agreement is shown only with the model that applies mean velocity and turbulence spectra, as the measured turbulence violates the scaling assumption in the second model. |
Observations and modeling of heat fluxes on tidal flats Rinehimer, J.P., and J. Thomson, "Observations and modeling of heat fluxes on tidal flats," J. Geophys. Res.,119, 133-146, doi:10.1002/2013JC009225, 2014. |
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1 Jan 2014 |
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A cross-shore model of tidal flat heat and mass fluxes is developed to understand the heat exchange between the sediment bed and the water column. A convective heat-transfer coefficient is used to model sediment-water heat fluxes which are as great as 20% of the incoming solar shortwave radiation. The model results match well with observations and are used to assess processes accross tidal to seasonal timescales. During the summer, tidal flat sediments store incoming shortwave radiation during exposure and act effectively as a net source of heat to the water column. This pattern changes in the winter, when the flats cool during exposure and act effectively as a net sink of heat. Additionally, during the summer water temperatures at the edge of the flooding front are elevated 5°C above the surface sediment temperatures. Model results replicate this process only when water column light extinction coefficients are high, consistent with visual observations of high turbidity (and thus high light absorption) at the leading edge of the flooding front. |
Quantifying upper ocean turbulence driven by surface waves D'Asaro, E.A., J. Thomson, A.Y. Shcherbina, R.R. Harcourt, M.F. Cronin, M.A. Hemer, and B. Fox-Kemper, "Quantifying upper ocean turbulence driven by surface waves," Geophys. Res. Lett, 41, 102-107, doi:10.1002/1013GL058193, 2014. |
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1 Jan 2014 |
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Nearly all operational ocean models use air-sea fluxes and the ocean shear and stratification to estimate upper ocean boundary layer mixing rates. This approach implicitly parameterizes surface wave effects in terms of these inputs. Here, we test this assumption using parallel experiments in a lake with small waves and in the open ocean with much bigger waves. Under the same wind stress and adjusting for buoyancy flux, we find the mixed layer average turbulent vertical kinetic energy in the open ocean typically twice that in the lake. The increase is consistent with models of Langmuir turbulence, in which the wave Stokes drift, and not wave breaking, is the dominant mechanism by which waves energize turbulence in the mixed layer. Applying these same theories globally, we find enhanced mixing and deeper mixed layers resulting from the inclusion of Langmuir turbulence in the boundary layer parameterization, especially in the Southern Ocean. |
Wave breaking dissipation in a young wind sea Schwendeman, M., J. Thomson, and J. Gemmrich, "Wave breaking dissipation in a young wind sea," J. Phys. Oceanogr., 44, 104-127, doi: 10.1175/JPO-D-12-0237.1, 2014. |
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1 Jan 2014 |
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Coupled in situ and remote sensing measurements of young, strongly forced wind waves are applied to assess the role of breaking in an evolving wave field. In situ measurements of turbulent energy dissipation from wave-following Surface Wave Instrument Float with Tracking (SWIFT) drifters and a tethered acoustic Doppler sonar system are consistent with wave evolution and wind input (as estimated using the radiative transfer equation). |
Inference of turbulence parameters from a ROMS simulation using the kε closure scheme Thyng, K.M., J.J. Riley, and J. Thomson, "Inference of turbulence parameters from a ROMS simulation using the kε closure scheme," Ocean Model., 72, 104-118, doi:10.1016/j.ocemod.2013.08.008, 2013. |
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1 Dec 2013 |
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Comparisons between high resolution turbulence data from Admiralty Inlet, WA (USA), and a 65-meter horizontal grid resolution simulation using the hydrostatic ocean modelling code, Regional Ocean Modeling System (ROMS), show that the model's kε turbulence closure scheme performs reasonably well. Turbulent dissipation rates and Reynolds stresses agree within a factor of two, on average. Turbulent kinetic energy (TKE) also agrees within a factor of two, but only for motions within the observed inertial sub-range of frequencies (i.e., classic approximately isotropic turbulence). TKE spectra from the observations indicate that there is significant energy at lower frequencies than the inertial sub-range; these scales are not captured by the model closure scheme nor the model grid resolution. To account for scales not present in the model, the inertial sub-range is extrapolated to lower frequencies and then integrated to obtain an inferred, diagnostic total TKE, with improved agreement with the observed total TKE. The realistic behavior of the dissipation rate and Reynolds stress, combined with the adjusted total TKE, imply that ROMS simulations can be used to understand and predict spatial and temporal variations in turbulence. The results are suggested for application to siting tidal current turbines. |
Method for identification of Doppler noise levels in turbulent flow measurements dedicated to tidal energy Richard, J-.B., J. Thomson, B. Polagye, and J. Bard, "Method for identification of Doppler noise levels in turbulent flow measurements dedicated to tidal energy," Int. J. Mar. Energy, 3-4, 52-64, doi:10.1016/j.ijome.2013.11.005, 2013. |
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1 Dec 2013 |
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Acoustic Doppler sensors used for flow measurements at energetic tidal sites present an inherent "Doppler noise" in the measured signal, varying with hardware configuration and flow conditions. At scales comparable to the sensors' sampling frequencies, the corresponding perturbations notably contaminate the signal, and cannot be corrected in the time series. |
Waves and the equilibrium range at Ocean Weather Station P Thomson, J., E.A. D'Asaro, M.F. Cronin, W.E. Rogers, R.R. Harcourt, and A. Shcherbina, "Waves and the equilibrium range at Ocean Weather Station P," J. Geophys. Res., 118, 5951-5962, doi:10.1002/2013JC008837, 2013. |
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1 Nov 2013 |
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Wave and wind measurements at Ocean Weather Station P (OWS-P, 50°N 145°W) are used to evaluate the equilibrium range of surface wave energy spectra. Observations are consistent with a local balance between wind input and breaking dissipation, as described by Philips (1985). The measurements include direct covariance wind stress estimates and wave breaking dissipation rate estimates during a 3 week research cruise to OWS-P. The analysis is extended to a wider range of conditions using observations of wave energy spectra and wind speed during a 2 year mooring deployment at OWS-P. At moderate wind speeds (515 m/s), mooring wave spectra are in agreement, within 5% uncertainty, with the forcing implied by standard drag laws and mooring wind measurements. At high wind speeds (>15 m/s), mooring wave spectra are biased low, by 13%, relative to the forcing implied by standard drag laws and mooring wind measurements. Deviations from equilibrium are associated with directionality and variations at the swell frequencies. A spectral wave hindcast accurately reproduces the mooring observations, and is used to examine the wind input. |
Sea State and Boundary Layer Physics of the Emerging Arctic Ocean: Science Plan Thomson, J., et al., "Sea State and Boundary Layer Physics of the Emerging Arctic Ocean: Science Plan," Technical Report, APL-UW TR1306, Applied Physics Laboratory, University of Washington, Seattle, September 2013, 59 pp. |
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16 Sep 2013 |
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The Office of Naval Research initiated a Department Research Initiative (DRI) titled Sea State and Boundary Layer Physics of the Emerging Arctic Ocean. The central hypothesis of the "Sea State" DRI is that surface waves now have a much greater role in the contemporary Arctic Ocean. Indeed, the entire Arctic Ocean in summer may soon resemble a marginal ice zone (MIZ), where waves propagate through the ice pack and affect the evolution of sea ice over large scales. |
An Evaluation of the U.S. Department of Energy's Marine and Hydrokinetic Resource Assessments Marine and Hydrokinetic Energy Technology Assessment Committee (including J. Thomson); Board on Energy and Environmental Systems; Division on Engineering and Physical Sciences; Ocean Studies Board; Division on Earth and Life Sciences; National Research Council, "An Evaluation of the U.S. Department of Energy's Marine and Hydrokinetic Resource Assessments," Washington, D.C.: The National Academies Press, 2013, 154 pp. |
1 Sep 2013 |
Resource mapping at tidal energy sites Palodichuk, M., B. Polagye, and J. Thomson, "Resource mapping at tidal energy sites," IEEE J. Ocean. Eng., 38, 433-446, doi:10.1109/JOE.2012.2227578, 2013. |
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1 Jul 2013 |
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Station keeping, a vessel-based spatial surveying method for resolving details of the hydrokinetic resource, is presented in the context of the general methodology and also for the specific case of a survey conducted in northern Admiralty Inlet, Puget Sound, WA, in June 2011. The acoustic Doppler current profiler (ADCP) measurements collected during the June 2011 survey were part of a broader effort to characterize the resource at this location before tidal turbine installation. Autonomous bottom-lander (bottom-mounted) ADCP measurements are used to evaluate the accuracy with which data collected from this vessel-based survey reflect stationary measurements and also to analyze the potential for cycle-to-cycle variations in the conclusions drawn. Results indicate good agreement between shipboard and bottom-mounted observations in capturing spatial resource differences. Repeated surveys over several tidal cycles are required to obtain results consistent with long-term observations. Station-keeping surveys help to optimize bottom-mounted ADCP deployments that are then used to estimate turbine power generation potential and make final siting decisions. |
Thermal observations of drainage from a mud flat Rinehimer, J. P., J. Thomson, and C.C. Chickadel, "Thermal observations of drainage from a mud flat," Cont. Shelf. Res., 60, S125-S135, doi:10.1016/j.csr.2012.11.001, 2013. |
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15 Jun 2013 |
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Incised channels on tidal flats create a complex flow network conveying water on and off the flat during the tidal cycle. In situ and remotely sensed field observations of water drainage and temperature in a secondary channel on a muddy tidal flat in Willapa Bay, Washington (USA) are presented and a novel technique, employing infrared imagery, is used to estimate surface velocities when the water depth in the channel becomes too shallow for ADCP measurements, i.e., less than 10 cm. Two distinct dynamic regimes are apparent in the resulting observations: ebb-tidal flow and the post-ebb discharge period. Ebb tide velocities result from the surface slope associated with the receding tidal elevation whereas the post-ebb discharge continues throughout the low tide period and obeys uniform open-channel flow dynamics. Volume transport calculations and a model of post-ebb runoff temperatures support the hypothesis that remnant water on the flats is the source of the post-ebb discharge. |
Sediment-generated noise and bed stress in a tidal channel Bassett, C., J. Thomson, and B. Polagye, "Sediment-generated noise and bed stress in a tidal channel," J. Geophys. Res., 118, 2249-2265, doi:10.1002/jgrc.20169, 2013. |
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30 Apr 2013 |
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Tidally driven currents and bed stresses can result in noise generated by moving sediments. At a site in Admiralty Inlet, Puget Sound, Washington State (USA), peak bed stresses exceed 20 Pa. Significant increases in noise levels are attributed to mobilized sediments at frequencies from 430 kHz with more modest increases noted from 14 kHz. Sediment-generated noise during strong currents masks background noise from other sources, including vessel traffic. Inversions of the acoustic spectra for equivalent grain sizes are consistent with qualitative data of the seabed composition. Bed stress calculations using log layer, Reynolds stress, and inertial dissipation techniques generally agree well and are used to estimate the shear stresses at which noise levels increase for different grain sizes. Regressions of the acoustic intensity versus near-bed hydrodynamic power demonstrate that noise levels are highly predictable above a critical threshold despite the scatter introduced by the localized nature of mobilization events. |
Implications of tidal phasing for power generation at a tidal energy site Polagye, B., and J. Thomson, "Implications of tidal phasing for power generation at a tidal energy site," in Proc., 1st Marine Energy Technology Symposium, MET13, 10-11 April, Washington, D.C., 2013. |
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10 Apr 2013 |
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Spatial resource gradients have been observed at a number of proposed tidal energy sites. However, these gradients are typically quantified using the first or second moments (i.e., mean or standard deviation) of time series which obscures information about the co%u2010temporal amplitude and phase variation. These co%u2010temporal variations have a number of interesting implications for power production from arrays of tidal turbines. Here, co%u2010temporal time series data from several locations in northern Admiralty Inlet, Puget Sound, Washington (USA) are used to investigate phase variations in kinetic power density over length scales of less than 5 km. Results demonstrate that large phase variations in kinetic power density are routinely produced by phase variations in the harmonic and aharmonic currents. However, exploiting these phase variations in a way that reduces power generation intermittency requires that locations which are out of phase have similar mean kinetic power density and intermittency. Further investigation of local phasing at tidal energy sites of commercial interest is recommended. |
Low-cost ultility-scale wave energy enabled by magnetostriction Nair, B., R. Shendure, J. Nachlas, A. Gill, Z. Murphree, J. Campbell, V. Challa, J. Thomson, J. Talbert, A. De Klerk, and C. Rusch, "Low-cost ultility-scale wave energy enabled by magnetostriction," Proc., 1st Marine Energy Technology Symposium, METS13, 10-11 April, Washington, D.C., 2013. |
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10 Apr 2013 |
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Oscilla Power, Inc. (OPI) is developing a patented magnetostrictive wave energy harvester (MWEH) that could enable the disruptively low-cost production of grid-scale electricity from ocean waves, a large-scale resource that is more predictable and more proximal to demand growth than solar or wind. Designed to operate cost-effectively across a wide range of wave conditions, the MWEH will be the first use of reverse magnetostriction for large-scale energy production. |
Tidal turbulence spectra from a compliant mooring Thomson, J., L. Kilcher, M. Richmond, J. Talbert, A. deKlerk, B. Polagye, M. Guerra, and R. Cienfuegos, "Tidal turbulence spectra from a compliant mooring," Proc., 1st Marine Energy Technology Symposium, METS2013, 10-11 April, Washington, D.C., 2013. |
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10 Apr 2013 |
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A compliant mooring to collect high frequency turbulence data at a tidal energy site is evaluated in a series of short demonstration deployments. The Tidal Turbulence Mooring (TTM) improves upon recent bottom-mounted approaches by suspending Acoustic Doppler Velocimeters (ADVs) at mid-water depths (which are more relevant to tidal turbines). The ADV turbulence data are superior to Acoustic Doppler Current Profiler (ADCP) data, but are subject to motion contamination when suspended on a mooring in strong currents. In this demonstration, passive stabilization is shown to be sufficient for acquiring bulk statistics of the turbulence, without motion correction. With motion correction (post-processing), data quality is further improved. Results from two field sites are compared, and the differences are attributed to the generation of large eddies by headlands and sills. |
A vessel noise budget for Admiralty Inlet, Puget Sound, Washington (USA) Bassett, C., B. Polagye, M. Holt, and J. Thomson, "A vessel noise budget for Admiralty Inlet, Puget Sound, Washington (USA)," J. Acoust. Soc. Am., 132, 3706-3719, doi:10.1121/1.4763548, 2012. |
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1 Dec 2012 |
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One calendar year of Automatic Identification System (AIS) ship-traffic data was paired with hydrophone recordings to assess ambient noise in northern Admiralty Inlet, Puget Sound, WA (USA) and to quantify the contribution of vessel traffic. The study region included inland waters of the Salish Sea within a 20 km radius of the hydrophone deployment site. Spectra and hourly, daily, and monthly ambient noise statistics for unweighted broadband (0.0230 kHz) and marine mammal, or M-weighted, sound pressure levels showed variability driven largely by vessel traffic. Over the calendar year, 1363 unique AIS transmitting vessels were recorded, with at least one AIS transmitting vessel present in the study area 90% of the time. A vessel noise budget was calculated for all vessels equipped with AIS transponders. Cargo ships were the largest contributor to the vessel noise budget, followed by tugs and passenger vessels. A simple model to predict received levels at the site based on an incoherent summation of noise from different vessels resulted in a cumulative probability density function of broadband sound pressure levels that shows good agreement with 85% of the temporal data. |
Wave breaking dissipation observed by SWIFT drifters Thomson, J., "Wave breaking dissipation observed by SWIFT drifters," J. Atmos. Ocean. Technol., 29, 1866-1882, doi:10.1175/JTECH-D-12-00018.1, 2012. |
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1 Dec 2012 |
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Energy dissipation rates during ocean wave breaking are estimated from high-resolution profiles of turbulent velocities collected within 1 m of the surface.The velocity profiles are obtained from a pulse-coherent acoustic Doppler sonar on a wave-following platform, termed a Surface Wave Instrument Float with Tracking, or "SWIFT", and the dissipation rates are estimated from the structure function of the velocity profiles. The purpose of the SWIFT is to maintain a constant range to the time-varying surface and thereby observe the turbulence in breaking crests (i.e., above the mean still water level). The Lagrangian quality is also useful to pre-filter wave orbital motions and mean currents from the velocity measurements, which are limited in magnitude by phase-wrapping in the coherent Doppler processing. Field testing and examples from both offshore whitecaps and nearshore surf breaking are presented. Dissipation is elevated (up to 10-3 m2 s-3) during strong breaking conditions, which are confirmed using surface videos recorded onboard the SWIFT. Although some velocity contamination is present from platform tilting and heaving, the structure of the velocity profiles is dominated by a turbulent cascade of eddies (i.e., the inertial sub-range). The noise, or uncertainty, in the dissipation estimates is shown to be normally distributed and uncorrelated with platform motion. Aggregated SWIFT measurements are shown to be useful in mapping wave breaking dissipation in space and time. |
Marginal Ice Zone (MIZ) Program: Science and Experiment Plan Lee, C.M., et al., "Marginal Ice Zone (MIZ) Program: Science and Experiment Plan," APL-UW TR 1201, Technical Report, Applied Physics Laboratory, University of Washington, Seattle, October 2012, 48 pp. |
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9 Oct 2012 |
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The Marginal Ice Zone (MIZ) intensive field program will employ an array of cutting-edge autonomous platforms to characterize the processes that govern Beaufort Sea MIZ evolution from initial breakup and MIZ formation though the course of the summertime sea ice retreat. Instruments will be deployed on and under the ice prior to initial formation of the MIZ along the Alaska coast, and will continue sampling from open water, across the MIZ, and into full ice cover, as the ice edge retreats northward through the summer. The flexible nature of ice-mounted and mobile, autonomous oceanographic platforms (e.g., gliders and floats) facilitates access to regions of both full ice cover and riskier MIZ regions. This approach exploits the extended endurance of modern autonomous platforms to maintain a persistent presence throughout the entire northward retreat. It also takes advantage of the inherent scalability of these instruments to sample over a broad range of spatial and temporal scales. |
Measurements of turbulence at two tidal energy sites in Puget Sound, WA Thomson, J., B. Polagye, V. Durgesh, M.C. Richmond, "Measurements of turbulence at two tidal energy sites in Puget Sound, WA," IEEE J. Ocean. Eng., 37, 363-374, doi:10.1109/JOE.2012.2191656, 2012. |
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15 May 2012 |
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Field measurements of turbulence are presented from two sites in Puget Sound, WA, that are proposed for electrical power generation using tidal current turbines. Time series data from multiple acoustic Doppler instruments are analyzed to obtain statistical measures of fluctuations in both the magnitude and direction of the tidal currents. The resulting turbulence intensities (i.e., the turbulent velocity fluctuations normalized by the deterministic tidal currents) are typically 10% at the hub heights (i.e., the relevant depth) of the proposed turbines. Length and time scales of the turbulence are also analyzed. Large-scale, anisotropic eddies dominate the turbulent kinetic energy (TKE) spectra, which may be the result of proximity to headlands at each site. At small scales, an isotropic turbulent cascade is observed and used to estimate the dissipation rate of TKE, which is shown to balance with shear production. Data quality and sampling parameters are discussed, with an emphasis on the removal of Doppler noise from turbulence statistics. The results are relevant to estimating the performance and fatigue of tidal turbines. |
Underwater noise measurements of a 1/7th scale wave energy converter Bassett, C., J. Thomson, B. Polagye, and K. Rhinefrank, "Underwater noise measurements of a 1/7th scale wave energy converter," In Proceedings, MTS/IEEE OCEANS 2011, Waikoloa, 19-22 September, doi:110.1109/OCEANS.2010.5664380 (MTS/IEEE, 2011). |
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22 Sep 2011 |
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Field measurements of the underwater acoustic signature of Columbia Power Technologies (Columbia Power) SeaRay wave energy converter (WEC) prototype are presented. The device was deployed in the vicinity of West Point (Puget Sound, Washington State) at a depth of approximately 20 meters. The 1/7th scale SeaRay prototype is a heave and surge, point absorber secured to the seabed with a three-point mooring. Acoustic measurements were made in order to satisfy permit requirements and assure that marine life is not adversely affected. A series of one-minute hydrophone recordings were collected on March 30, 2011 for approximately 4 hours. During these recordings, significant wave height varied from 0.4 to 0.7 m, peak wave periods varied from 2.9 to 3.2 seconds, and southerly winds varied from 5 to 10 m s-1. These are approximately twice the amplitude of typical operating conditions for the SeaRay in Puget Sound. Shipping vessel and ferry traffic levels also were typical. Received sound pressure levels during the experiment vary from 116 to 132 dB re 1 µPa in the integrated bands from 20 Hz to 20 kHz. At times, ship traffic dominates the signal, as determined from spectral characteristics and vessel proximity. Received sound pressure levels attributed to the WEC cycle from 116 to 126 dB re 1 µPa in the integrated bands from 60 Hz to 20 kHz at distances from 10 to 1500 m from the SeaRay. The cycling is well correlated with the peak wave period, including peaks and harmonics in the pressure spectral densities. Masking by ship noise prevents rigorous extrapolation to estimate the WEC source level at the conventional 1 m reference. |
Characterizing underwater noise at a proposed tidal energy site in Puget Sound Bassett, C., J. Thomson, and B. Polagye, "Characterizing underwater noise at a proposed tidal energy site in Puget Sound," In Proceedings, MTS/IEEE Oceans 2010, 20-23 September, doi:10.1109/OCEANS.2010.5664380 (MTS/IEEE, 2010). |
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20 Sep 2010 |
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Ambient underwater acoustics data are presented for one year at a potential tidal energy site in Admiralty Inlet, WA (USA) with maximum currents exceeding 3 m/s. The site, at a depth of approximately 60 meters, is located near shipping lanes, a local ferry route, and a transit area for many cetacean species. A key finding is that the statistical distribution of total sound pressure levels are dependent on tidal currents at the site. Pseudosound, cobbles shifting on the sea bed, and vibrations induced by forces on the equipment are possible explanations. Non-propagating turbulent pressure fluctuations, termed pseudosound, can mask ambient noise, especially in highly energetic environments suitable for tidal energy development. |
Limits to the predictability of tidal current power Polagye, B., J. Epler, and J. Thomson, "Limits to the predictability of tidal current power," In Proceedings, MTS/IEEE Oceans 2010, Seattle, 20-23 September doi:10.1109/OCEANS.2010.5664588 (MTS/IEEE, 2010). |
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20 Sep 2010 |
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The predictability of tidal currents in the context of hydrokinetic power generation are assessed using current data from a series of surveys in Admiralty Inlet, Puget Sound, Washington, USA. Both current speed and kinetic power density are shown to be well-described by harmonic analysis. Three challenges to predictability are identified. First, non-sinusoidal fluctuations over time scales on the order of hours are observed but cannot be replicated by conventional harmonic analysis. Second, turbulent fluctuations over time scales on the order of seconds are relatively large and inherently unpredictable. Third, for this site, predictions may not be extrapolated more than 100 m from the location of measurement. While none of these issues are insurmountable, they contribute to a degree of unpredictability for tidal hydrokinetic power. |
Quantifying turbulence for tidal power applications Thomson, J., M. Richmond, B. Polagye, and V. Durgesh, "Quantifying turbulence for tidal power applications," In Proceedings, MTS/IEEE OCEANS 2010, Seattle, 20-23 September, doi:10.1109/OCEANS.2010.5664600 (MTS/IEEE, 2010). |
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20 Sep 2010 |
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Using newly collected data from a tidal power site in Puget Sound, WA, metrics for turbulence quantification are assessed and discussed. Of particular interest is the robustness of the "turbulent intensity," defined as the ratio of velocity standard deviation to velocity mean. Simultaneously, the quality of raw ping Acoustic Doppler Current Profiler (ADCP) data for turbulence studies is evaluated against Acoustic Doppler Velocimeter (ADV) data at a point. Removal of Doppler noise from the raw ping data is shown to be a crucial step in turbulence quantification. Excluding periods of slack tide, the corrected turbulent intensity estimates at a height of 4.6 m above the seabed are 10% and 11% from the ADCP and ADV, respectively. Estimates of the turbulent dissipation rate are more variable, from 10-3 to 10-1 W/m3. An example analysis of coherent Turbulent Kinetic Energy (TKE) is presented. |
Shipboard acoustic Doppler current profiler surveys to assess tidal current resources Epler, J. B. Polagye, and J. Thomson, "Shipboard acoustic Doppler current profiler surveys to assess tidal current resources," In Proceedings, MTS/IEEE Oceans 2010, Seattle, 20-23 September, doi:10.1109/OCEANS.2010.5664387 (MTS/IEEE, 2010). |
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20 Sep 2010 |
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A compelling aspect of power generation from tidal currents is the predictability of the resource, which is generated by the gravitational pull of the sun and moon on the earth's oceans. For technical feasibility studies, it is presupposed that once the currents at a site have been well characterized it is possible to make accurate predictions of the electricity that would be generated by an array of turbines. These data are generally collected by Acoustic Doppler Current Profilers (ADCP), which use active acoustics to measure currents throughout the water column. |
Observations of thermal diffusivity and a relation to the porosity of tidal flat sediments Thomson, J., "Observations of thermal diffusivity and a relation to the porosity of tidal flat sediments," J. Geophys. Res., 115, doi:10.1029/2009JC005968, 2010. |
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19 May 2010 |
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Time series observations of vertical profiles of sediment temperature are presented for several locations at two distinct tidal flats. Surface sediment temperatures are shown to be strongly dependent on solar insolation during low-tide exposure, and that signal is communicated to the subsurface sediment temperatures. A vertical diffusion balance explains the observations well (up to 97% of the observed variance at some locations and 76% on average), and an estimate of thermal diffusivity is obtained for each location. A theoretical model relating sediment porosity to thermal diffusivity is presented and shown to agree with independent estimates of porosity. In addition, thermal diffusivity is shown to correlate with direct observations of sediment composition (percent sand) and surface strength. Results are suggested for application to remote classification of sediments using infrared time series images. |
Site characterization for tidal power Gooch, S., J. Thomson, B. Polagye, and D. Meggitt, "Site characterization for tidal power," In Proceedings, MTS/IEEE Oceans 2009, Biloxi, MS, 26-29 October (MTS/IEEE, 2009). |
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26 Oct 2009 |
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Tidal In-Stream Energy Conversion (TISEC) is a promising source of clean, renewable and predictable energy. One of the preliminary steps in developing the technology is establishing a standardized and repeatable methodology for the characterization of potential deployment sites. Stationary Acoustic Doppler Profiler (ADCP) velocity data collected at four sites near Marrowstone Island, Puget Sound are used to test the applicability of metrics characterizing maximum and mean velocity, eddy intensity, rate of turbulent kinetic energy dissipation, vertical shear, directionality, ebb and flood asymmetry, vertical profile and other aspects of the flow regime deemed relevant to TISEC. |
A fourier-based method for the distribution of breaking crests from video observations Thomson, J., and A.T. Jessup, "A fourier-based method for the distribution of breaking crests from video observations," J. Atmos. Ocean. Technol., 26, 1663-1671, doi:10.1175/2009JTECHO622.1, 2009. |
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1 Aug 2009 |
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A Fourier-based method is presented to process video observations of water waves and calculate the speed distribution of breaking crest lengths. The method has increased efficiency and robust statistics compared with conventional algorithms that assemble distributions from tracking individual crests in the time domain. The method is tested using field observations (video images of whitecaps) of fetch-limited breaking waves during case studies with low (6.7 m s-1), moderate (8.5 m s-1), and high (12.6 m s-1) wind speeds. The method gives distributions consistent with conventional algorithms, including breaking rates that are consistent with direct observations. Results are applied to obtain remote estimates of the energy dissipation associated with wave breaking. |
Energy dissipation and the spectral distribution of whitecaps Thomson, J., J.R. Gemmrich, and A.T. Jessup, "Energy dissipation and the spectral distribution of whitecaps," Geophys. Res. Lett, 36, doi:10.1029/2009GL038201, 2009. |
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3 Jun 2009 |
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Energy dissipation by breaking water waves is quantified indirectly using remote observations (digital video recordings) and directly using in situ observations (acoustic Doppler velocity profiles). The analysis is the first validation using field data to test the Duncan-Phillips formulation relating energy dissipation to the spectral distribution of whitecap speeds and lengths. Energy dissipation estimates are in agreement over two orders of magnitude, and demonstrate a promising method for routine observation of wave breaking dynamics. Breaking statistics are partitioned into contributions from waves at the peak of the wave-height spectrum and waves at higher frequencies in the spectrum. Peak waves are found to be only 10% of the total breaking rate, however peak waves contribute up to 75% of the total dissipation rate. In addition, breaking statistics are found to depend on the peak wave steepness and the energy input by the wind. |
Refraction and reflection of infragravity waves near submarine canyons Thomson, J., S. Elgar, T.H.C. Herbers, B. Raubenheimer, and R.T. Guza, "Refraction and reflection of infragravity waves near submarine canyons," J. Geophys. Res., 112, doi:10.1029/2007JC004227, 2007. |
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10 Oct 2007 |
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The propagation of infragravity waves (ocean surface waves with periods from 20 to 200 s) over complex inner shelf (water depths from about 3 to 50 m) bathymetry is investigated with field observations from the southern California coast. A wave-ray-path-based model is used to describe radiation from adjacent beaches, refraction over slopes (smooth changes in bathymetry), and partial reflection from submarine canyons (sharp changes in bathymetry). In both the field observations and the model simulations the importance of the canyons depends on the directional spectrum of the infragravity wave field radiating from the shoreline and on the distance from the canyons. Averaged over the wide range of conditions observed, a refraction-only model has reduced skill near the abrupt bathymetry, whereas a combined refraction and reflection model accurately describes the distribution of infragravity wave energy on the inner shelf, including the localized effects of steep-walled submarine canyons. |
In The News
Why physicists are air-dropping buoys into the paths of hurricanes New Scientist, James Dinneen A sprawling research program aims to improve hurricane forecasts by collecting data at the chaotic interface of ocean and atmosphere. |
20 Sep 2024
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NOAA researchers study sea ice retreat, link to harmful algal blooms The Nome Nuggest, Colin A. Warren Last week a team of National Oceanic and Atmospheric Administration researchers arrived in Nome to launch the third year of an investigation that seeks to study sea ice retreat and chart phytoplankton in the northern Bering Sea. |
14 Jun 2024
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Hyperspectral cameras and high-tech buoys: Inside NOAA's Arctic AIR mission KNOM Radio, Nome, AK, Ben Townsend A project called 'Arctic AIR' is back in the Bering and Chukchi seas this summer to conduct studies of sea ice retreat and phytoplankton. The researchers seek to better understand rapid changes occurring in the Arctic's marine ecosystem due to climate change. |
7 Jun 2024
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UW-developed wave sensors deployed to improve hurricane forecasts UW News Jacob Davis, a UW doctoral student in civil and environmental engineering, and members of the U.S. Navy’s VXS-1 Squadron deployed wave sensing buoys in the path of Hurricane Ian, before the hurricane made landfall. |
28 Sep 2022
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See delicate rib vortices encircle breaking ocean waves Scientific American, Joanna Thompson These little-studied mini twisters form beautiful loops under the water’s surface. Until the past decade or so few people in the scientific community paid much attention to rib vortices, partly because they are difficult to photograph. The ephemeral twists require a high-resolution camera and precise timing to capture. |
1 Aug 2022
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U.S. icebreaker gap with Russia a growing concern as Arctic 'cold war' heats up Washington Times, Mike Glenn Warming trends have spurred a chase for trade routes, natural resources at top of the world. Vessels like the Healy and the Polar Star are the most effective tools for maintaining access to the icy regions for scientific, economic and security purposes, advocates say. |
23 Sep 2021
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Spiraling Crisis: The Alarming Convergence of Climate Change and Pandemics ThinkTech Hawaii In this video documentary available on YouTube, Jim Thomson is interviewed to share the impacts of the pandemic on his research into coastal ocean dynamics in the Arctic. |
16 Aug 2021
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Using advanced acoustic technology to understand wave conditions and climate change in the Arctic Environment Coastal & Offshore, Torbjørn Goa Thomson’s research in the Arctic has paired Nortek Signature500 acoustic Doppler current profilers (ADCPs) mounted on fixed moorings with drifters equipped with Signature1000 ADCPs to get a complete picture of the Arctic’s changing wave conditions. |
29 Mar 2021
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TECH FILE: Acoustic tech used to understand climate change in the Arctic Marine Technology News Major changes are occurring in the ocean. Climate change and subsequent melting sea ice are not necessarily good changes. Why are acoustic Doppler current profilers an invaluable tool to get a complete picture of the Arctic’s changing wave conditions in the context of climate change? |
27 Mar 2021
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Advanced acoustic technology to understand wave conditions and climate change in the Arctic Hydro International Acoustic Doppler current profilers are an invaluable tool to get a complete picture of the Arctic's changing wave conditions in the context of climate change. |
26 Mar 2021
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Understanding wave conditions and climate change in the Arctic with acoustic technology Ocean News & Technology Moorings equipped with upward-facing Signature500 ADCPs provide a long time series of data. The instruments, which collect data on the waves, currents and sea ice when it is present, are duty-cycled to record data every hour. |
25 Mar 2021
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Coast Guard icebreaker Polar Star departs Seattle for important arctic mission KING 5 News (Seattle), Glenn Farley The Seattle-based Polar Star has several important duties in the Arctic, including sending a strong message to Russia and conducting unique research. |
4 Dec 2020
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UW study finds disturbing climate change evidence in Arctic Ocean KING5 News, Glenn Farley A joint study between the University of Washington and University of Alaska has uncovered the presence of 'pancake ice' and tall waves in the Arctic Ocean. Photo: John Guillotte |
21 Jan 2020
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Warm ocean water delays sea ice for Alaska towns, wildlife Associated Press, Dan Joling In the new reality of the U.S. Arctic, open water is the November norm for the Chukchi. Instead of thick, years-old ice, researchers are studying waves and how they may pummel the northern Alaska coastline. |
19 Nov 2019
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Fall storms, coastal erosion focus of northern Alaska research cruise UW News, Hannah Hickey A University of Washington team is leaving to study how fall storms, dwindling sea ice and vulnerable coastlines might combine in a changing Arctic. The project leaves Thursday, Nov. 7, from Nome, Alaska in the Bering Strait to spend four weeks gathering data during the fall freeze-up season. |
5 Nov 2019
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Floating wind digital twin set to accelerate wave impact learnings New Engery Update, Reuters A new digital twin project led by floating wind developer Principle Power will use advanced wave behavior analysis to improve load calculations critical to long-term design efficiency. DIGIFLOAT will use a network of linked offshore buoys developed by APL-UW to measure and predict a range of incoming wave metrics at the site. The buoys also measure profiles of ocean currents and turbulence. |
23 Oct 2019
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UW team sending autonomous surfboard to explore Antarctic waters UW News, Hannah Hickey The research project will use the Wave Glider to investigate the summer conditions near Palmer Station on the Antarctic Peninsula, to better understand how the warming ocean interacts with ice shelves that protrude from the shore. It will then head across Drake Passage, braving some of the stormiest seas on the planet. |
23 Oct 2019
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Public talks kick off study of ice loss, warming and coastal changes in northern Alaska UW News The northernmost town in the country had its warmest March on record. Utqiagvik, formerly known as Barrow, is among the coastal communities that are feeling the effects of a warming Arctic firsthand. |
25 Apr 2019
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State investigators focus on nets plugged with mussels in Atlantic salmon net-pen failure The Seattle Times, Lynda Mapes Cooke Aquaculture’s maintenance practices at its collapsed Atlantic salmon farm at Cypress Island have drawn the attention of state investigators after nets were found fouled with mussels and other sea life. Fluid mechanics expert Jim Thomson notes that nets clogged with sea life create greater drag forces in the ocean currents, increasing the risk of structural failure. |
26 Jan 2018
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Partners in Extreme Wave Modeling Engineering Out Loud Podcast, Jens Odegaard How do you forecast and model huge waves in the open ocean? As part of the National Marine Renewable Energy Center, researchers at Oregon State University and the University of Washington are modeling and forecasting extreme waves to help inform wave energy technology. |
25 Oct 2017
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Wave Glider surfs across stormy Drake Passage in Antarctica UW News, Hannah Hickey The University of Washington sent a robotic surf board to ride the waves collecting data from Antarctica to South America. |
20 Sep 2017
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Validating tall tales of rogue waves Hakai Magazine, Mara Johnson-Groh Recently, scientists took to the seas, using sensors to monitor more than two million waves in a bid to identify the oceanic conditions that create rogue waves. |
13 Mar 2017
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The balance of ice, waves, and winds in the Arctic autumn EOS Earth & Space Science News, Jim Thomson, Stephen Ackley, Hayley Shen, and Erick Rogers Although summer sea ice loss in the Arctic is well studied, less is known about how ice comes back in autumn. A new program, Sea State and Boundary Layer Physics in the Emerging Arctic Ocean, is changing that. |
23 Jan 2017
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With new tech, scientists probe what lies beneath the Sound The Herald (Everett), Chris Winters The Adaptable Monitoring Package (AMP) undergoes tests near Sequin, WA. Instrumented with two kinds of sonar, a current profiler, three visual cameras, and four hydrophones, it can bes used for basic research on the health of the Puget Sound ecosystem or other projects requiring undersea monitoring for long periods of time. |
17 Jan 2016
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Wish you were here: Arctic explorer CNN Jim Thomson shows what it's like to measure waves in the Arctic Ocean. |
3 Dec 2014
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Coupeville ferry gets high-tech addition to help scientists Everette Herald Both ferries on the Coupeville to Port Townsend route will now pull double-duty thanks to sensors installed on their hulls. The ferries are helping to monitor water quality in Puget Sound for the Department of Ecology and APL-UW. |
14 Nov 2014
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U.S. Navy awards $8 million to develop wave, tidal energy technology UW News and Information, Hannah Hickey The U.S. Navy has committed to get half of its energy from renewable sources by the year 2020. The University of Washington is helping to reach that goal with an $8 million, four-year contract from the Naval Facilities Engineering Command, or NAVFAC, to develop marine renewable energy for use at the Navy's facilities worldwide. |
24 Oct 2014
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Surf's up in the Arctic: Record-high waves seen in 2012 Fox News, Becky Oskin Record-high waves hit Alaska's Beaufort Sea in September 2012, when Arctic sea ice shrank to an extreme summer low, a new study reports. |
4 Aug 2014
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Huge waves in the Arctic demonstrate ice loss and aggravate it Slate, Eric Holthaus The house-sized waves measured by oceanographer Jim Thomson and his research team during a Beaufort Sea storm in 2012 are bigger than any seen before in that part of the Arctic, where it's warmer now than at any point since humans began living there 44,000 or so years ago. Previously, there was just too much ice for waves to form. |
1 Aug 2014
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16-foot waves in the Arctic: A harbinger of ice-free summers? Christian Science Monitor, Pete Spotts Until recently, the Arctic Ocean's central Beaufort Sea was ice-covered throughout the summer. But with a greater expanse of open water, scientists are tracking how waves and well-traveled swells could accelerate the loss of summer ice. |
30 Jul 2014
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Giant waves found in Arctic Ocean could be accelerating sea ice loss The Washington Post Capital Weather Gang, Angela Fritz Huge areas of ice-free water are leading to massive waves in the Arctic Ocean, according to a study published in Geophysical Research Letters. |
30 Jul 2014
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Sixteen-foot swells reported in once-frozen region of Arctic Ocean The Washington Post, Fred Barbash The fact that researchers have now measured swells of more than 16 feet in the Arctic's Beaufort Sea, just north of Alaska, is a bit of a stunner. Swells of that size, researchers say, have the potential to break up Arctic ice even faster than the melt underway there for decades thanks to rapid global warming. |
30 Jul 2014
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Huges waves measured for first time in Arctic Ocean UW News and Information, Hannah Hickey Arctic ice used to retreat less than 100 miles from the shore. In 2012, it retreated more than 1,000 miles. Wind blowing across an expanse of water for a long time creates whitecaps, then small waves, which then slowly consolidate into big swells that carry huge amounts of energy in a single punch. |
29 Jul 2014
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Sensor-equipped ferry to monitor Admiralty Inlet, gateway to Puget Sound Environmental Monitor, Daniel Kelly Newly installed acoustic sensors on two Washington ferries will help monitor water circulation in Puget Sound. Scientists with the Applied Physics Laboratory at the University of Washington will manage the monitoring effort that relies on acoustic doppler current profilers to measure a host of environmental parameters. |
30 Jun 2014
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Puget Sound monitoring The Impact @ TVW (video), Jennifer Huntley The state ferry system is working with scientists to learn more about the water in Puget Sound. Find out about a new high-tech water monitoring device aboard the ferries. |
18 Jun 2014
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Ferries for science: Instrument will monitor flow in Puget Sound UW News and Information, Hannah Hickey It%u2019s not just vacationers who will be traveling on the ferries between Port Townsend and Coupeville this summer. A new partnership among the Washington Department of Ecology, the University of Washington and other groups is riding on Washington State Ferries to improve understanding of water circulation in Puget Sound. |
16 Jun 2014
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Feds approve Puget Sound tidal energy project KUOW Radio, Courtney Flatt A proposal for the world%u2019s first grid-connected tidal energy project received a federal license. The project has been almost eight years in the making. |
20 Mar 2014
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Beyond the forecast: Power play KING5 News, Seattle Washington State is on the forefront of green energy production, including harnessing winds, tides, and sunlight to produce electricity. |
23 Nov 2013
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A tide of local influences The New York Times Scientist at Work Blog, Jim Thomson Principal Oceanographer Jim Thomson blogs from the Canal de Chacao in Chile. His research team is measuring the tidal turbulence in the channel to determine if the area is suitable for power generating turbine installation. |
27 Feb 2013
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Noisy ships, ferries create racket below Puget Sound The Seattle Times, Craig Welch Recent work by University of Washington researchers shows noise in some Puget Sound shipping channels regularly meets or exceeds levels the federal government suggests may be harmful to marine life. |
3 Jan 2013
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Heading home, and hanging ten The New York Times, Jim Thomson Principal Oceanographer Jim Thomson and his research team set out in the North Pacific in hopes of finding big storms and big waves. His NY Times "Scientist at Work" blog chronicles their search for the big waves and what the instruments they deploy into them tell us about the turbulence created by breaking waves in the open ocean. |
17 Oct 2012
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Ocean energy is a vast, unproven resource The Kitsap Sun Jim Thomson, a University of Washington researcher, is studying the potential energy that can be produced at Admiralty Inlet and the potential environmental effects. When the project started three years ago, almost nothing was known about that area of Puget Sound, he said. |
9 Nov 2011
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IBM sees energy, money in motion of the ocean MSNBC, John Roach APL-UW's Jim Thomson is helping characterize the noise environment in Admiralty Inlet in Washington's northern Puget Sound for a pilot project with a local utility that will install underwater turbines to capture energy from the tides. |
1 Nov 2011
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Renewable tidal energy's reality check CNN Money Jim Thomson and his research team have been collecting data for nearly three years at a potential undersea tidal energy site in Admiralty Inlet. The data will inform the best practices for harnessing tidal energy at the site when the turbines are lowered to the bottom and connected to the power grid. |
20 Oct 2011
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Harnessing tides in the northwest KUOW Radio The sun is setting as the Jack Robertson, a 65-foot research vessel, leaves the harbor. Two spidery-looking orange pieces of machinery, each one weighing about 1,000 pounds, crouch on the back deck. These sea spiders, as they're called, are for measuring tidal currents and more. |
24 Aug 2011
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Will oceans' tides supply endless electricity? Bellingham Herald, Rob Hotakainen, McClatchy Newspapers Two large hydro turbines will be installed 200 feet deep in the harsh waters of Admiralty Inlet by late summer 2013, marking the first project of its kind in Washington state. But before then, scientists want to figure out how rockfish, diving birds, whales and other marine life will respond to the intruding turbines. |
6 Aug 2011
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Admiralty Inlet ocean life studied to accommodate potential undersea turbine generators Peninsula Daily News, Charlie Bermant Four submerged data collection devices were retrieved in Admiralty Inlet off the shore of Whidbey Island on Wednesday as scientists prepare to monitor ocean life around turbine electrical generators. |
9 Jun 2011
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Data from Puget Sound's depths tell of marine life at proposed turbine site Kitsap Sun, John Stang Engineers aboard the University of Washington research vessel Jack Robertson hauled up a rig that looks like a squat three-legged spider that stores numerous gigabytes of raw data. Researchers will now take the data and study it to learn about sea life in the area where turbines for tidal energy are planned. |
8 Jun 2011
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Is tidal energy affecting sea life? KING 5 News, Gary Chittim Revolutionary efforts to harness the power of Puget Sound tides took a big step forward today. Sophisticated imaging devices have been hard at work studying the possible effects of large scale underwater energy production. They are looking at how a grid of generators might harm sensitive sea life including endangered salmon and orcas. |
8 Jun 2011
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Researchers Study Potential Impact Of Tidal Power Turbines OPB News, Ashley Ahearn Powerful tides of the Strait of Juan de Fuca suggest this is a perfect place to harness energy. Jim Thomson, oceanographer at the Applied Physics Laboratory, University of Washington is leading the feasibility research. |
24 May 2011
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Admiralty Inlet an ideal spot for tidal power KOMO News Nearly two years of monitoring show the Admiralty Inlet is an ideal place to harness tidal energy, University of Washington researchers say. |
14 Dec 2010
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Assessing the environmental effects of tidal turbines UW News and Information, Hannah Hickey Harnessing the power of ocean tides has long been imagined. A demonstration project planned for Puget Sound will be the first tidal energy project on the west coast of the United States, and the first array of large-scale turbines to feed power from ocean tides into an electrical grid. |
13 Dec 2010
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Camera paints colorful orca portrait King 5 News, Gary Chittim UW researchers detect resident Orca whale images at night using infrared camera technology. This tool will help ensure that whale pods are not harmed as tidal energy projects are developed in the Puget Sound. |
26 Aug 2010
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Currents of Change Seattle Business Magazine, Amelia Apfel Local experts rely on teamwork and patience to bring tidal power to the Northwest. |
1 Jul 2010
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What exactly is the 'Vashon Hum'? The Seattle Post-Intelligencer, AMELIA HEAGERTY The "Vashon Hum" is a very low pure tone that people have heard all across the Island in Puget Sound. APL-UW engineers and oceanographers weigh in on likely and unlikely sources. |
15 Apr 2010
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UW scientists discover mud flats produce fresh water KING 5 News, Gary Chittim Jim Thomson and his team made a discovery on the mud flats of Willapa Bay. Buried within the insulating mud of the flats is a reservoir of warm, fresh water that is constantly flowing into streams and the ocean. |
5 Apr 2010
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Post-Enron, Snohomish County utility cultivates own energy The Daily News Online, Phuong Le, The Associated Press This year, the utility received nearly $1 million from the federal government for a pilot project to install tidal turbines in Puget Sound and to test-drill for geothermal hot spots in the region. |
4 Jul 2009
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Tidal-energy project stays on course after UW's tests on Puget Sound The Seattle Times, Michelle Ma Researchers from the University of Washington spent four days last week on board a vessel collecting data, capturing underwater video and measuring velocity in Admiralty Inlet between Port Townsend and Whidbey Island. The channel likely will host one of the nation's largest tidal-energy projects. |
15 Apr 2009
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Concerns emerge about environmental effects of wave-energy technology The Seattle Times, Michelle Ma Energy generated from the ocean's waves and tides might be the next source of "green" power in our region, but the technology demands more study. A new marine renewable-energy research center has been launched, giving the University of Washington the lead for tidal-power research. |
17 Nov 2008
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