Sack Lunch Seminar (SLS)

Distinct influence of air-sea coupling mediated by mesoscale SST and surface current in the two summer boundary current systems

The two summertime boundary current systems, the California Current in the North Pacific and the Somali Current in the western Indian Ocean, are characterized by the energetic surface velocity and vigorous coastal upwelling with a rich filamentary eddy structure. The associated large anomalies and gradients of surface current and SST modify the surface stress, triggering so-called mesoscale air-sea interactions. This presentation will discuss results from high-resolution regional coupled model simulations with a scale-separation of the air-sea coupling, showing that mesoscale air-sea interactions through SST and surface current exert dynamically distinct influences on the energetics of these boundary current systems. Effect of SST-wind coupling is manifested most strongly in the Ekman pumping velocity, which primarily affects the position of the eddy fields but not their amplitude. In contrast, the current-wind coupling substantially reduces the total wind work, thus the mean and eddy kinetic energy. The vorticity-induced Ekman pumping through the current-wind coupling further attenuates the eddy amplitude. Significant time-mean responses in SST and evaporation are found due to the current-wind coupling in the Arabian Sea, suggesting its potential importance to downstream atmospheric monsoon circulation.