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Influence of the Distortion of Vertical Wavenumber Spectra on Estimates of Turbulent Dissipation Using the Finescale Parameterization: Observations in the Antarctic Circumpolar Current
Author(s) -
Takahashi Anne,
Hibiya Toshiyuki
Publication year - 2021
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2020jc016613
Subject(s) - wavenumber , internal wave , spectral line , dissipation , turbulence , wave packet , spectral slope , geology , geostrophic wind , geophysics , physics , computational physics , shear (geology) , mesoscale meteorology , atmospheric sciences , mechanics , climatology , optics , petrology , quantum mechanics , astronomy , thermodynamics
Finescale parameterizations are powerful tools for estimating the global distribution of turbulent kinetic energy dissipation rates ɛ . However, they tend to overestimate ɛ in the Antarctic Circumpolar Current (ACC), where bottom‐reaching mesoscale eddies coexist with energetic internal waves such as wind‐induced near‐inertial waves and bottom‐generated internal lee waves. In this study, we explore the reason for such overestimations by analyzing simultaneous microstructure and finestructure measurements in the ACC. Finescale parameterizations overestimate ɛ where vertical wavenumber spectra of internal wave energy are distorted from the canonical Garrett‐Munk (GM) spectrum by a spectral hump at ∼0.01 cpm wavenumbers. Since shear and strain spectra are integrated over the noise‐free wavenumbers lower than the rolloff wavenumber, the spectral levels are overestimated for such spectra. These distorted shear spectra are mainly located in the upper ocean, while distorted strain spectra near the seafloor. Correlation analyses suggest that shear and strain spectral humps are caused by near‐inertial and lee wave packets superposed on a GM‐like internal wave field, and these wave packets are generated or amplified by geostrophic shear flows.