Atmospheric Adjustments Drive Long‐Term Weakening of the Zonal Sea Surface Temperature Gradient in the Tropical Atlantic

Abstract

Multiple observational records indicate a long‐term weakening of the zonal sea surface temperature (SST) gradient in the tropical Atlantic, characterized by enhanced warming in the east. However, the underlying mechanism remains elusive as the concurrent strengthening of the surface southeasterlies and the zonal tilt of the equatorial thermocline would suggest a strengthened zonal gradient through Bjerknes feedback. Here, we demonstrate that this zonal SST gradient weakening is instead driven by local atmospheric adjustments, which are mainly contributed by latent heat flux changes. In the west, intensified surface southeasterlies—linked to a strengthened regional Hadley circulation—suppress local warming by reducing surface relative humidity and increasing surface wind speed. In the east, horizontal moisture convergence increases local relative humidity to enhance local warming. Our findings highlight the critical role of local atmospheric adjustments in shaping the historical tropical Atlantic SST warming pattern, which is distinct from coupled air–sea dynamics.