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

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.