Inferring diapycnal mixing using the internal wave continuum from the high resolution ocean model

Abstract

Internal wave (IW)-induced mixing plays a crucial role in maintaining the thermohaline circulation. However, as most ocean general circulation models (OGCMs) do not resolve the scales of IWs and turbulence, to appropriately express the IW-induced turbulent dissipation is a long-lasting issue for ocean model development. Here we report the estimates of IW-induced turbulent dissipation in the South China Sea (SCS), from a tide-included OGCM using an internal wave continuum parameterization scheme (IWCP). The estimation is based on the energy level of internal wave continuum (IWC), by converting the finescale parameterization (FSP) from wavenumber to the frequency domain. The estimated dissipation rates are elevated over the Luzon Strait (LS), northern SCS, and continental slopes, up to O(10⁻⁷) Wkg⁻¹ between 100 and 500 m depth, while those in the central basin of SCS are O(10⁻¹⁰) Wkg⁻¹. The performance of IWCP are evaluated against observational datasets (Argo, CTD based FSP estimates, and CTD based Thorpe scale method estimates) and tidal-mixing parameterization schemes. The errors in IWCP's results are comparable with the discrepancies among different observational datasets. The IWCP significantly outperforms the widely used tidal mixing parameterization that only considers local internal tides, and are comparable, if not superior, to the tidal mixing parameterization that consider both local and non-local generation, depending on the choice of benchmark observational datasets. This work illustrates that IWCP could be an alternative efficient mean to estimate the three-dimensional map of IW-induced mixing from the high resolution OGCM.