Examining Turbulence and Vortex Structures in the Wake of Velasco Reef Near Palau.

Bethan Wynne-Cattanach1, Matthew H Alford2, Jennifer A MacKinnon3, Jonathan D Nash4 and Gunnar Voet3, (1)Scripps Institution of Oceanography, UC San Diego, La Jolla, United States, (2)Scripps Institution of Oceanography, La Jolla, CA, United States, (3)Scripps Institution of Oceanography, La Jolla, United States, (4)Oregon State University, Corvallis, United States
Abstract:
Both tidal and low-frequency flows interact strongly with abrupt topographic features, giving rise to a variety of small-scale phenomena including lee waves, vortical motions and turbulence. With the goal of identifying the processes that transfer momentum and energy between the larger-scale and smaller-scale flows, detailed tidally-resolving shipboard surveys were conducted in the vicinity of Velasco reef, a sharp and steep headland near Palau, in 2016 as part of the FLow Encountering Abrupt Topography (FLEAT) program. We present microstructure and rapid-cycling CTD/ADCP measurements, contextualized with five nearby 10-month long moored records, in order to examine wake and vortex structures. Mean flow is layered and multi-directional in depth, such that "downstream" of the headland depends on the depth. Turbulence in each layer is complicated and arising from an interaction of near-inertial, tidal and mean flows, but is generally elevated 1-2 orders of magnitude downstream of the headland, and associated with sharp O(1 km) vortices. In this study we examine the magnitude, patterns and causes of the vortices and elevated turbulence.