Effects of Surface Heating on Coastal Upwelling Intensity

Abstract

Numerical experiments were conducted to evaluate the effects of surface heating on coastal upwelling intensity. Offshore transport, isopycnal slope, and the sea surface temperature (SST) difference between coastal and offshore regions, which represent the upwelling intensity, were estimated. Surface heating decreases Ekman transport but increases Ekman pumping by changing air-sea stability conditions. However, offshore transport does not change significantly with surface heating. Our experimental results revealed that the increase in surface heating decreases the isopycnal slope but increases the SST difference. Both the isopycnal slope and SST difference are closely related to the change in the surface boundary layer (SBL). Strong surface heating thins the surface-mixed layer, which decreases the vertical eddy viscosity. The decreased vertical eddy viscosity thins the SBL and enhances its offshore velocity. The isopycnal slope weakens because of the thin SBL, while the SST difference becomes stronger because of the enhanced offshore velocity despite the same offshore transport. The present study may be relevant to the change in upwelling systems as the increase in surface heating under future global warming.