Submesoscale activity associated with the São Tomé Cape Cyclone: a numerical study

Abstract

The Brazil Current (BC) is the western boundary current that closes the South Atlantic Subtropical Gyre. Between 22æS and 23æS, the BC forms large cyclonic meanders, in particular, off Cape Frio and São Tomé Cape. The system of high vertical shear, formed by the BC and the underlying northward flow of the Intermediate Western Boundary Current (IWBC) are responsible for forming, in this region, baroclinic instabilities that generate these great meanders. Eventually, these cyclones advect mass and volume from the continental shelf to more oceanic regions and induce local upwelling, that alters the local biogeochemical dynamics. However, although these mesoscale processes are important for regional biogeochemical processes, the typical mesoscale vertical velocities are an order of magnitude lower than the submesoscale processes vertical velocities (a scale that is on the threshold between the small scale three-dimensional movements and the horizontally isotropic and hydrostatic movements of the quasi-geostrophic dynamics). These submesoscale movements are considered more important for local biogeochemical processes. Due to this importance, this work aims to present a first description of the submesoscale activity that is developed in the São Tomé Cape Cyclone. The intention is to characterize and describe the submesoscale hydrodynamic processes, such as edge eddies and filaments, that can affect regional biogeochemical dynamics. To this end, a simulation of a regional hydrodynamic model, with horizontal resolution capable of solving submesoscale processes (between 500 m and 2 km) will be built in order to simulate a formation event of the São Tomé Cape Cyclone observed in December 2019 during the Ilhas 3 oceanographic cruise (FAPESP Proc. 2015/21729-4). With this simulation, the submesoscale processes, and the submesoscale features and instabilities developed in the cyclone will be investigated and described. (AU)