72 / 2023-07-27 16:20:25

Diapycnal mixing observed in an anticyclonic eddy in the northwestern South China Sea

diapycnal mixing,anticyclonic eddy,energy transition

The dissipation rate of turbulent kinetic energy was directly measured cross an anticyclonic eddy in spring of 2018 on the shelf and slope of northwestern South China Sea. The eddy was generated to the northwest of Luzon Strait and its western periphery was approaching Xisha during the observation. Maxima of salinity and current velocity in the subsurface layer and double-pycnocline structure on the shelf indicate the existence of submesoscale coherent vortex. The magnitude of dissipation rate at the periphery of eddy was in the order of 10^-9 W kg^-1, enhanced values were detected mainly in the mixed layer over the shelf and over the bottom of the slope, strongly dependent on the gradient Richardson number on the shear instability. The elevated mixing was consistent with the downward propagation of near-inertial energy related to wind stress and baroclinic tidal energy over topography derived from synchronous mooring observations. Moreover, double-diffusion convection was also responsible for the elevated dissipation rate between the pycnoclines and in the interior.