Coupled modeling of eddy-wind interaction in the California Current System

The California Current System is characterized by energetic mesoscale and filamentary eddies, which are important for ecosystem variability in this region. Recent high-resolution satellite observations show that these mesoscale eddies significantly modify the Ekman pumping velocity through their effect of mesoscale SST and surface current anomalies on wind stress, suggesting that the eddy-wind interaction might be an important mechanism for the eddy dynamics. The relative importance of effects of mesoscale SST and currents is however not well known. Here, we use the high-resolution fully-coupled Scripps Coupled Ocean-Atmosphere Regional (SCOAR) model to address this question by implementing a novel coupling technique that selectively isolates the coupling effect by mesoscale SST and currents. The result shows that eddy kinetic energy (EKE) is reduced by >20% when the eddy-wind coupling is allowed, and this reduction is almost entirely due to the effect of eddy-induced currents on the stress. Eddy-current effect also leads to Ekman pumping velocity that is twice as strong (30 cm/day) as that by SST effect. The significant reduction of EKE and the increase in Ekman pumping velocity by the mesoscale current suggests that ocean modeling studies will need to parameterize the effect of air-sea velocity difference in the calculation of surface stress to more accurately simulate the eddy dynamics and their impact on the mean state.