We examine the statistical characteristics of ocean wave breaking and associated turbulent dissipation rates in a field of intermittent events. The intent is to reconcile the field measurements of surface following drifters (SWIFTs) with numerical model results and dynamic scalings. Conversion of the model results to a surface-following reference frame, along with normalizing of the model domain to match observations of whitecap coverage, are essential steps. We show that convergence of statistics occurs after approximately 1000 randomly spaced observations in time and space, relative to 3D breaking events. We further show important effects of 1) anisotropy in the calculation of the scalar turbulent dissipation rates, 2) vertical extent of measurements with depth, 3) obscuration of velocity measurements due to entrained bubbles. Most importantly, the numerical model confirms that high dissipation occurs preferentially with high void fractions (i.e., within bubble plumes). Results are scaled with wave steepness, following the conventional formulation for breaking strength. We also examine an analogy of turbulent dissipation rates for waves in partial sea ice cover.
Speaker bio:
Jim is a Senior Principal Oceanographer in the Applied Physics Laboratory at the University of Washington in the U.S. and is also an Associate Professor in the university’s Civil and Environmental Engineering Department. http://apl.uw.edu/people/profile.php?last_name=Thomson&first_name=Jim
Jim’s research interests are in environmental fluid mechanics, ocean waves, marine renewable energy, waves in polar regions and instrument development.
A particular focus of his interest is measuring turbulence in the upper 1 m of the ocean water column using bespoke SWIFT drifters, making him and his group the global leaders in turbulence measurements in this challenging environment. http://www.apl.washington.edu/project/project.php?id=swift