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



[1] 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.