Surface conditions associated with anomalous rainfall in the Guinea coastal region.

Abstract

This paper examines surface atmospheric and oceanic conditions associated with anomalous rainfall at the Guinea coast. For time‐scales shorter than 5 years, rainfall in the Guinea coast is practically not correlated with rainfall in the Sahel, although both time series show a well‐defined drying trend in the last 30 years or so. While interannual variability of Sahel rainfall is associated with a sea‐surface temperature (SST) pattern anti‐symmetric about the Equator, anomalous rainfall near the Guinea coast in associated with an SST pattern roughly symmetric about the Equator. During wet years near the Guinea coast this SST pattern corresponds to a less developed cold tougue in the boreal summer. Using the Comprehensive Ocean‐Atmosphere Data Set surface fields we examine key terms of the oceanic heat budget. Anomalous shortwave radiation and latent heat fluxes seem to play an important role in the decaying of the SST anomaly. During wet years anomalous atmospheric winds act to relax the trade winds, which probably reduces the equatorial thermocline slope and contributes to the observed warming of the equatorial waters in the east. We also investigate the relationship between the surface winds and the underlying SST using numerical and analytical solutions of a simple model. The anomalous winds are shown to be consistent with the hydrostatic adjustment of the tropical boundary layer.