Seasonality of the SST-precipitation relationship over the North Tropical Atlantic and its possible mechanisms

Based on the monthly sea surface temperature (SST) data from the Met Office Hadley Centre, the Global Precipitation Climatology Project monthly precipitation data, and the historical simulations from Coupled Model Intercomparison Project Phase 6 climate models, the present work investigates the seasonality of SST-precipitation relationship over the North Tropical Atlantic (NTA) and possible role of ENSO (El Ni?o-Southern Oscillation) in it. It is found that the relationship of SST anomalies in the NTA with local precipitation exhibits a remarkable seasonality. During spring and summer, there is a strong positive correlation between SST and precipitation in this region, indicating a strong local ocean-atmosphere coupling. In contrast, in autumn and winter, the ocean-atmosphere coupling weakens significantly, and almost no significant precipitation response to SST is detected. Further analysis reveals that this seasonality is mainly associated with the seasonal cycle of the background SST and local SST variability in the NTA. Despite cooler background SST in spring, the strong SST variability during this season makes SST easy to exceed the convection threshold and thus induce precipitation anomalies. In summer, the warm background SST favors in the enhanced local ocean-atmosphere coupling. The relatively decreased SST variability in autumn weakens the local precipitation response, despite with a relatively warm SST background. In contrast to summer, the cooler background SST in winter results in a weak ocean-atmosphere coupling. Since the impact of ENSO on tropical Atlantic precipitation is mainly located south of 5°N, there is almost no difference in the local ocean-atmosphere coupling in the tropical North Atlantic with or without ENSO SST forcing. These findings emphasize the critical role of spring and summer NTA SST anomalies in local convection and associated climate impacts, which is of significant importance for short-term climate prediction related to the NTA SST.