Assessment of fine‐scale parameterizations of turbulent dissipation rates near mixing hotspots in the deep ocean

Abstract

Shear‐based and/or strain‐based fine‐scale parameterizations of turbulent dissipation rates in the deep ocean become erroneous near topographic features where internal wave spectra deviate from Garrett‐Munk (GM). Although the Gregg‐Henyey‐Polzin (GHP) parameterization incorporates this spectral deviation, the applicability remains uncertain. We evaluate “α” and “β” representing the local internal wave energy in the high frequency (2f < ω < N) and low frequency (f < ω < 2f) bands, respectively, scaled by their corresponding values in GM using fine‐scale vertical shear and strain simultaneously measured near mixing hotspots. The local internal wave spectra are biased toward higher frequencies (α/β ≫ 1) over rough bathymetry where high frequency internal waves are generated, whereas they are biased toward lower frequencies (α/β≪ 1) at latitudes where high vertical wavenumber, near‐inertial shears are created byparametric subharmonic instabilities. Compared with the shear‐based and/or strain‐based parameterizations, GHP more accurately estimates turbulent dissipation rates by compensating for deviations from GM.