Seasonal cycle of sea surface temperature and air-sea interactions in the Northwest African upwelling region

The upwelling region off northwest Africa exhibits pronounced seasonal variability and high productivity, playing a critical role in supporting fisheries. The sea surface temperature (SST) difference between the coast and offshore areas serves as a key proxy for upwelling intensity. Using observational data, we found distinct regional dependencies in the response of SST differences to atmospheric forcing. In the permanent upwelling region (21°N-30°N), both upwelling-favorable winds and heat flux enhance the coastal-offshore SST difference, leading the variations by about 70-100 days. In contrast, in the seasonal upwelling region (12°N-19°N),  changes in SST differences precede wind variations by less than one month, particularly during the transition to the downwelling season. Heat flux in this region acts to dampen SST gradients, contrasting with its role in the permanent upwelling zone. Additionally, our results indicate that the response of the SST difference to atmospheric forcing is faster and stronger when the mixed layer is shallower. These results highlight the spatial variability and complexity of air-sea interactions in the northwest African upwelling system, with implications for understanding coastal upwelling dynamics and informing fisheries management.