Mechanisms of a shelf submesoscale front in the northern South China Sea

Abstract

Ocean fronts are important dynamic processes that occur at various scales. Submesoscale fronts (Rossby number, Ro≈1) associated with strong vertical velocity easily induce high chlorophyll-a concentrations within the upper ocean. However, direct observations of the submesoscale front in the shelf of northern South China Sea are scare, and the dynamic process of submesoscale front is still unclear. Based on 1 km high-spatial resolution in situ data, we investigated a submesoscale front and examined its frontogenesis and frontolysis mechanisms. The observed submesoscale front had a Rossby number of O(1) and Richardson number of Ri < 1 (strong vertical shear). During the frontolysis process, mixed symmetric and centrifugal instabilities were triggered within the entire water column, and symmetric instability was triggered by topography gradient. Mixed-layer baroclinic instabilities (MLIs) was also significant in frontogenesis process, and the large buoyancy flux triggered by wind speed was possibly the energy source for MLIs. This study provides direct observational evidence of the submesoscale front and its energy source, which can improve our understanding of submesoscale processes.