Warm events in the Tropical Atlantic

Sea surface temperature in the eastern equatorial Atlantic Ocean undergoes anomalous warming events of 1 degree -2 degree C every few years. The warm anomalies reach their maximum strength in Northern Hemisphere summer, when equatorial upwelling normally brings cold thermocline water to the surface. By compositing surface observations from a 28-year record, we are able to identify consistent features in anomalies of SST and winds. The composites show that the SST anomalies in northern summer are confined to the eastern equatorial region, with reduced zonal winds to the west and reduced northward trade winds to the east. Accompanying these changes in winds are enhanced convection near the equator caused by a southward shift and intensification of the intertropical convergence zone. Later in the year, SST south of the equator becomes elevated. As a result, by spring of the year following the equatorial anomaly, convection in the western side of the basin is much higher than normal.