Small-Scale Processes in the COASTal Ocean

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Observations made as part of the COAST (Coastal Ocean Advances in Shelf Transport) project by the Ocean Mixing Group at Oregon State University have already led to new insights into the details of coastal flows. These are an extensive set of observations obtained over a broad range of both topography and flow states. The data are of uniformly high quality and include new types of measurements implemented specifically for this experiment (e.g., high-frequency Doppler velocity profiling and turbulence measurements from a bottom lander) which have enhanced our ability to infer the small-scale dynamics of these flows. However, due to the extensive nature of this data set a number of key issues still need to be addressed.In this study, a researcher at Oregon State University will continue his analysis of the small-scale COAST data set to determine a useful parameterization of small-scale topographic drag and mixing that can be used in coastal ocean circulation models; this will be done using the comprehensive bottom boundary layer data that includes near-bottom stratification, turbulence dissipation rate and current speeds over a broad range of bathymetry. A detailed characterization of mixing during downwelling, including an analysis of the dynamics of merged surface and bottom boundary layers will be constructed. The researcher will also assess the interaction of near-inertial waves and internal tide with the coastal jet and how the presence of the coastal jet alters mixing parameterizations that are based primarily on wave shear. Finally, both the energetic evolution of bottom-trapped nonlinear internal waves/bores of elevation and the net mass transports by these waves will be quantified. The primary objective of the work is to understand the flow physics to sufficiently aid in parameterizations, which can then be applied to coastal ocean models. In this way, the analyses of the physics of small-scale processes will contribute to our understanding of the larger scale circulation. A graduate student will also be trained on how to bridge the gap between small-scale dynamics and their parameterization in terms of larger-scale variables.