Influence of the vertical resolution when simulating ocean sound speed variability in mesoscale eddies

Abstract

Vertical resolution affects the representation of ocean sound speed according to a suite of regional simulations of the De Soto Canyon circulation in the Gulf of Mexico. Simulations have identical horizontal resolution of 0.5 km, partially resolving submesoscale dynamics, and increasing vertical resolution from 30 (i.e., comparable to what commonly used in mesoscale permitting or resolving hindcast and forecast products such as HYCOM) to 200 terrain-following layers. Simulations with 30- and 70-layers underestimate the ageostrophic contributions in and around the eddies below the mixed-layer and do not reproduce the sharp vorticity and density variations associated with the mesoscale circulations compared to the 140- and 200-layers runs. The ocean sound speed (based on the classical MacKenzie formula) was found to be far more variable when the submesoscale, ageostrophic circulations are captured also in their vertical structure and vertical contributions to the density field. Hence, the results of this study indicate that to better predict the influence of the submesocale oceanic circulation on ocean sound speed variability, model simulations should consider enhancing both horizontal and vertical resolution to resolve at least the first 3 baroclinic modes. To do so, more than 100 vertical layers were found to be needed in this study.