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Michael Schwendeman

Research Associate

Email

mschwendeman@apl.washington.edu

Phone

206-616-6359

Publications

2000-present and while at APL-UW

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

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.

Observations of whitecap coverage and the relation to wind stress, wave slope, and turbulent dissipation

M. Schwendeman, 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

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 6–14 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.

More Info

28 Dec 2015

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 6–14 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.

More Publications

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

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.

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

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.

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

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

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.

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

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).

The Phillips breaking crest distribution Λ(c) is calculated using stabilized shipboard video recordings and the Fourier-based method of Thomson and Jessup, with minor modifications. The resulting Λ(c) are unimodal distributions centered around half of the phase speed of the dominant waves, consistent with several recent studies. Breaking rates from Λ(c) increase with slope, similar to in situ dissipation. However, comparison of the breaking rate estimates from the shipboard video recordings with the SWIFT video recordings show that the breaking rate is likely underestimated in the shipboard video when wave conditions are calmer and breaking crests are small. The breaking strength parameter b is calculated by comparison of the fifth moment of Λ(c) with the measured dissipation rates. Neglecting recordings with inconsistent breaking rates, the resulting b data do not display any clear trends and are in the range of other reported values. The Λ(c) distributions are compared with the Phillips equilibrium range prediction and previous laboratory and field studies, leading to the identification of several inconsistencies.

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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