Finescale measurements of Kelvin-Helmholtz instabilities at a Kuroshio seamount

Data supporting the results presented in 'Finescale measurements of Kelvin-Helmholtz instabilities at a Kuroshio seamount', Journal of Physical Oceanography DOI 10.1175/JPO-D-24-0235.1

Fine-scale properties of Kelvin–Helmholtz (KH)-like shear instabilities on the trailing edge of a nonlinear lee wave generated by the Kuroshio impinging on a seamount were measured using a towed CTD chain, shipboard ADCP, and echosounder. Lee-wave vertical velocity amplitudes vary in phase with the upstream semidiurnal along-stream current. The instabilities are analogous to atmospheric billows induced by a recirculation on the trailing edge of mountain lee waves. A total of 135 KH billows were identified in a 4-day-long time series roughly 300 m downstream of the center of the lee wave. The KH billows have heights H=52+-11 m, widths L=162+-72 m, and aspect ratios H/L=0.39+-0.18. Positive reduced shear squared S2-4N2 (where S is the vertical shear magnitude and N is the buoyancy frequency) in the shear-stratified billows suggests actively growing instabilities, with comparable contributions from across- and along-flow vertical shear. Billow cores are convectively unstable (N2<0). Large turbulent kinetic energy dissipation rates O(10-5) W/kg are inferred from density overturns. Density, shear, and inferred turbulence properties vary with billow aspect ratios. As H/L increases, density gradients smear out. For 122 billows with H/L<0.6, dissipation rates increase by one order of magnitude with increasing H/L. These observations of 1-m vertical and 5-m horizontal resolution billow structures and density overturn dissipation rates can provide a reference for future high-Reynolds-number direct numerical simulations.