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James Girton

Principal Oceanographer

Affiliate Assistant Professor, Oceanography

Email

girton@uw.edu

Phone

206-543-8467

Research Interests

Overflows and Deep-Water Formation, Internal Waves, Mesoscale Eddies, Oceanic Surface and Bottom Boundary Layers, Measurements of Ocean Velocity Through Motionally-Induced Voltages

Biosketch

James Girton's research primarily investigates ocean processes involving small-scale turbulence and mixing and their influence on larger-scale flows. An important part of physical oceanography is the collection of novel datasets to shed new light on important physical processes, and to this end Dr. Girton's research has frequently drawn upon the widely under-utilized electromagnetic velocity profiling technique developed by Tom Sanford (his Ph.D. advisor and frequent collaborator). Instruments utilizing this technique include the expendable XCP, the full-depth free-falling AVP, and the autonomous long-duration EM-APEX. Each of these instruments has a unique role to play in the study of phenomena ranging from deep boundary currents and overflows to upper ocean mixing and internal waves.

In addition to being less well-understood elements of ocean physics, many of these phenomena are potentially important for the behavior of the large-scale ocean circulation, particularly the meridional overturning that transports heat to subpolar and polar regions and sequesters atmospheric gases in the deep ocean. Prediction of future climate change by coupled ocean-atmosphere models requires reliable predictions of ocean circulation, so physically-based improvements to parameterizations of mixing, boundary stresses and internal waves in such models are an ongoing goal.

Department Affiliation

Ocean Physics

Education

B.A. Physics, Swarthmore College, 1993

Ph.D. Oceanography, University of Washington, 2001

Projects

Sampling Quantitative Internal-wave Distributions — SQUID

Our goals are to understand the generation, propagation, and dissipation mechanisms for oceanic internal gravity waves to enable seamless, skillful modeling & forecasts of these internal waves between the deep ocean and the shore.

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26 Feb 2024

The SQUID team will provide a globally distributed observing program for shear, energy flux, and mixing by internal waves. We will use profiling floats — measuring temperature, salinity, velocity, and turbulence — that will yield new insights into internal wave regimes and parameterizations, and that will provide direct and derived data products tailored for use by modeling groups for comparison and validation. Data Sharing @ UW/Girton

Wave Glider Observations in the Southern Ocean

A Wave Glider autonomous surface vehicle will conduct a summer-season experiment to investigate ocean–shelf exchange on the West Antarctic Peninsula and frontal air–sea interaction over both the continental shelf and open ocean.

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4 Sep 2019

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.

Submesoscale Mixed-Layer Dynamics at a Mid-Latitude Oceanic Front

SMILE: the Submesoscale MIxed-Layer Eddies experiment

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1 Mar 2017

This experiment is aimed at increasing our understanding of the role of lateral processes in mixed-layer dynamics through a series of ship surveys and Lagrangian array deployments. Instrument deployments and surveys target the upper ocean's adjustment to winter atmospheric forcing events in the North Pacific subtropical front, roughly 800 km north of Hawaii.

This study will improve understanding of 1–10-km scale lateral processes in three-dimensional mixed-layer dynamics in a region of above-average atmospheric forcing, typical mid-ocean mesoscale advection and straining, and typical submesoscale activity. The results will improve the physical basis of mixed-layer parameterizations, leading to better model predictions of air-sea fluxes, gas transfer, and biological productivity.

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Publications

2000-present and while at APL-UW

Seasonal variability of near-inertial/semidiurnal fluctuations and turbulence in the subarctic North Atlantic

Kunze, E., R.-C. Lien, C.B. Whalen, J.B. Girton, B. Ma, and M.C. Buijsman, "Seasonal variability of near-inertial/semidiurnal fluctuations and turbulence in the subarctic North Atlantic," J. Phys. Oceanogr., 53, 2717-2735, doi:10.1175/JPO-D-22-0231.1, 2023.

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1 Dec 2023

Six profiling floats measured water-mass properties (Т, S), horizontal velocities (u, v) and microstructure thermal-variance dissipation rates χT in the upper ~1 km of Iceland and Irminger Basins in the eastern sub-polar North Atlantic from June 2019 to April 2021. The floats drifted into slope boundary currents to travel counterclockwise around the basins. Pairs of velocity profiles half an inertial period apart were collected every 7–14 days. These half-inertial-period pairs are separated into subinertial eddy (sum) and inertial/semidiurnal (difference) motions. Eddy flow speeds are ~O(0.1 m s-1) in the upper 400 m, diminishing to ~O(0.01 m s-1) by ~800-m depth. In late summer through early spring, near-inertial motions are energized in the surface layer and permanent pycnocline to at least 800-m depth almost simultaneously (within the 14-day temporal resolution), suggesting rapid transformation of large-horizontal-scale surface-layer inertial oscillations into near-inertial internal waves with high vertical group velocities through interactions with eddy vorticity-gradients (effective β). During the same period, internal-wave vertical shear variance was 2–5 times canonical midlatitude magnitudes and dominantly clockwise-with-depth (downward energy propagation). In late spring and early summer, shear levels are comparable to canonical midlatitude values and dominantly counterclockwise-with-depth (upward energy propagation), particularly over major topographic ridges. Turbulent diapycnal diffusivities K ~O(10-4 m2 s-1) are an order of magnitude larger than canonical mid-latitude values. Depth-averaged (10–1000 m) diffusivities exhibit factor-of-three month-by-month variability with minima in early August.

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

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.

Energy and momentum of a density-driven overflow in the Samoan Passage

Voet, G., and 8 others including J.B. Girton, "Energy and momentum of a density-driven overflow in the Samoan Passage," J. Phys. Oceanogr., 53, 1429-1452, doi:10.1175/JPO-D-22-0220.1, 2023.

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1 Jun 2023

The energy and momentum balance of an abyssal overflow across a major sill in the Samoan Passage is estimated from two highly resolved towed sections, set 16 months apart, and results from a two-dimensional numerical simulation. Driven by the density anomaly across the sill, the flow is relatively steady. The system gains energy from divergence of horizontal pressure work Ο(5)kW m-1 and flux of available potential energy Ο(2)kW m-1. Approximately half of these gains are transferred into kinetic energy while the other half is lost to turbulent dissipation, bottom drag, and divergence in vertical pressure work. Small-scale internal waves emanating downstream of the sill within the overflow layer radiate Ο(1)kW m-1 upward but dissipate most of their energy within the dense overflow layer and at its upper interface. The strongly sheared and highly stratified upper interface acts as a critical layer inhibiting any appreciable upward radiation of energy via topographically generated lee waves. Form drag of Ο(2)N m-2, estimated from the pressure drop across the sill, is consistent with energy lost to dissipation and internal wave fluxes. The topographic drag removes momentum from the mean flow, slowing it down and feeding a countercurrent aloft. The processes discussed in this study combine to convert about one-third of the energy released from the cross-sill density difference into turbulent mixing within the overflow and at its upper interface. The observed and modeled vertical momentum flux divergence sustains gradients in shear and stratification, thereby maintaining an efficient route for abyssal water mass transformation downstream of this Samoan Passage sill.

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In The News

Fact check: Video shows 'bono wave' tidal bore, not HAARP-generated phenomena

USA Today, Eleanor McCrary

A viral video shared on social media shows a naturally occurring tidal bore on the Kampar River in Indonesia. James Girton serves as one of the fact-check sources.

11 Apr 2023

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

One year into the mission, autonomous ocean robots set a record in survey of Antarctic ice shelf

UW News, Hannah Hickey

A team of ocean robots deployed in January 2018 have, over the past year, been the first self-guided ocean robots to successfully travel under an ice sheet and return to report long-term observations.

23 Jan 2019

More News Items

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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