Identify the diapycnical eddy diffusivities by salt fingers and turbulence with vertical microstructure measurements

Abstract

Diapycnical eddy diffusivities are formulated from physical relations according to a simple fact that the different formulas are identical for the same parameter. It is found that the dispassion ratio Γis a crucial parameter. When it is above a critical value (about 0.2), the flow is salt finger type; otherwise, it is turbulence. All the density ratio $R_{\rho }=1/(1-{\Gamma }^2)$, eddy flux ratio $\gamma =1/(1+\Gamma )$, and eddy diffusivity ratio $R_k=1-\Gamma$ are simply dependent on the dispassion ratio gamma Γ. We apply these relations to the measurement data in the western tropical Atlantic Ocean. The effective diapycnal diffusivity is $0.96\ast 10^{-4}{m}^2/s$ that agrees quite well with the observation from 0.8 to $0.9\ast 10^{-4}{m}^2/s$ by tracer.

6 pages, 1 figure