Intraseasonal modulation of Sea Surface Temperatures in the North Tropical Atlantic by African Easterly Waves

Résumé

Abstract. The sea surface temperature (SST) variability in the North Tropical Atlantic plays a crucial role in the regional climate by modulating the Intertropical Convergence Zone (ITCZ) and influencing precipitation, convective systems, and tropical cyclones. While atmospheric synoptic-scale intraseasonal variability in this region is dominated by African Easterly Waves (AEWs), their impact on SST remains poorly understood. This study investigates the modulation of SST by AEWs using a regional configuration of a coupled ocean-atmosphere model and PIRATA mooring air-sea observations. Results reveal a significant AEWs signature in SST anomalies, with temperature fluctuations exceeding ±0.5 °C. A heat budget analysis shows that AEWs mainly influence SST through modulation of the latent heat flux, shortwave radiation, and vertical mixing. The contribution of the ocean mixing and that of the air-sea fluxes appear of similar order, likely reflecting the influence of near-inertial currents. The dominant 3–5-day AEWs exhibit a stronger impact than their 6–9-day counterparts. These findings highlight the role of AEWs in driving SST variability and mixed-layer dynamics, underscore the importance of accurately representing them in coupled climate models, and call for further investigation into their influence on the mean and seasonal upper-ocean state.

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