Air-sea feedback in the northeastern tropical Atlantic in boreal summer at intraseasonal time-scales

This study analyzes air-sea interaction in the northeast tropical Atlantic (NETA) at intraseasonal time-scales, focusing on the feedback between sea-surface temperature (SST) and surface winds in July, August, and September, using observational data from 2009 to 2020 (Reynolds SST and advanced scatterometer surface winds) and European Centre for Medium-Range Weather Forecasts Reanalysis v5 data from 2000 to 2020. The analysis reveals that anomalies in the northeastern trade winds over the NETA, often associated with an African easterly wave, result in warmer SST when winds weaken and cooler SST when they intensify. In turn, this SST anomaly modulates surface wind anomalies, generating a negative feedback loop that lasts for 2-3 weeks. A secondary positive feedback loop at the northern edge of the SST anomaly contributes to this prolonged persistence and results in a slow northward migration of the coupled SST-sea-level-pressure gradient pattern. A warm SST anomaly between 5 degrees N and 15 degrees N therefore alters the propagating pattern of easterly waves by creating a negative pressure anomaly, enhancing moisture transport convergence off the West African coast and intensifying precipitation. It potentially contributes to the seasonal northward migration of the intertropical convergence zone from early to mid boreal summer. This study highlights the importance of better understanding these air-sea interaction processes and their representation in operational forecasting models to improve weather forecasts in the western Sahel region.