Evidence of enhanced double-diffusive convection below the main stream of the Kuroshio Extension
Evidence of enhanced double-diffusive convection below the main stream of the Kuroshio Extension
Abstract:
In this study, a Navis-MicroRider microstructure float and an EM-APEX float were deployed along the Kuroshio Extension Front. The observations deeper than 150 m reveal widespread interleaving thermohaline structures for at least 900 km along the front, presumably generated through mesoscale stirring and near-inertial oscillations.
In these interleaving structures, microscale thermal dissipation rates χ are very high O(>10-7 K2s-1), while turbulent kinetic energy dissipation rates ε are relatively low O(10-10-10-9 Wkg-1), with effective thermal diffusivity Kθ of O(10-3 m2s-1) consistent with the previous parameterizations for double-diffusion, and, Kθ is two orders of magnitude larger than the turbulent eddy diffusivity for density Kρ. The average observed dissipation ratio Γ in salt finger and diffusive convection favorable conditions are 1.2 and 4.0, respectively, and are larger than that for turbulence. Our results indicate that mesoscale subduction/obduction and near-inertial motions catalyze double-diffusive favorable conditions, and thereby enhancing the diapycnal tracer fluxes below the Kuroshio Extension Front.
In these interleaving structures, microscale thermal dissipation rates χ are very high O(>10-7 K2s-1), while turbulent kinetic energy dissipation rates ε are relatively low O(10-10-10-9 Wkg-1), with effective thermal diffusivity Kθ of O(10-3 m2s-1) consistent with the previous parameterizations for double-diffusion, and, Kθ is two orders of magnitude larger than the turbulent eddy diffusivity for density Kρ. The average observed dissipation ratio Γ in salt finger and diffusive convection favorable conditions are 1.2 and 4.0, respectively, and are larger than that for turbulence. Our results indicate that mesoscale subduction/obduction and near-inertial motions catalyze double-diffusive favorable conditions, and thereby enhancing the diapycnal tracer fluxes below the Kuroshio Extension Front.