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

TL;DR

This paper develops a method to identify diapycnal eddy diffusivities using microstructure measurements, distinguishing salt finger and turbulence regimes based on the dispassion ratio, and applies it to Atlantic Ocean data.

Contribution

It introduces a new approach linking physical relations to determine eddy diffusivities and the dispassion ratio's role in differentiating flow types.

Findings

Effective diffusivity measured as 0.96×10^{-4} m^2/s

Flow type depends on dispassion ratio  above 0.2 is salt finger

Relations agree with tracer-based observations

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 \Gamma is 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 \Gamma. We apply these relations to the measurement data in the western tropical Atlantic Ocean. The effective diapycnal diffusivity is $0.96*10^{-4} m^2/s$ that agrees quite well with the observation from 0.8 to $0.9*10^{-4} m^2/s$ by tracer.