Isopycnal Transport and Mixing of Tracers by Submesoscale Flows Formed at Wind-Driven Ocean Fronts

Abstract

Abstract : This project is part of the DRI on Scalable Lateral Mixing and Coherent Turbulence that aims to characterize lateral mixing in the ocean on scales of 10m-10 km, the submesoscales. Lateral mixing at the submesoscales is not accounted for in present-day ocean models. This deficiency is a potential source of error in the numerical prediction of the distribution of temperature, salt, nutrients, phytoplankton, pollutants, etc. in the upper ocean. The goal of the DRI is to develop parameterizations for submesoscale processes to improve the simulation of lateral mixing in ocean models. Winds blowing along ocean fronts are highly effective at energizing flows on the submesoscale. The process involves three stages: a frontal mixing stage where small scale gravitational and symmetric instabilities homogenize properties in the mixed layer, a subduction phase where threedimensional baroclinic mixed layer instabilities exchange fluid along isopycnal between the mixed layer and pycnocline, and a phase in which the mixed layer instabilities evolve into coherent vortices that drive lateral stirring along surfaces of constant density. The objective of this research is to characterize and parameterize the submesoscale physics involved in each of these steps and evaluate the lateral mixing characteristic of the flows in each stage. Dynamical insights gained from the research will be used for planning, interpreting, and analyzing observations collected during the two field programs that will be conducted as part of the DRI.