Finescale Measurements of Kelvin–Helmholtz Instabilities at a Kuroshio Seamount
Journal
Journal of Physical Oceanography
Journal Volume
55
Journal Issue
11
Start Page
2097
End Page
2117
ISSN
0022-3670
1520-0485
Date Issued
2025-11
Author(s)
Vladoiu, Anda
Lien, Ren-Chieh
Kunze, Eric
Ma, Barry
Essink, Sebastian
Chen, Jia-Lin
Yang, Kai-Chieh
Yeh, Yu-Yu
Abstract
Finescale 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) Wkg-1 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.
Subjects
Mixing
Shear structure/flows
Turbulence
Publisher
American Meteorological Society
Type
journal article