Anomalous Atmospheric Circulation Associated with Recent West African Monsoon Rainfall Variability

Abstract

The recent West African Monsoon (WAM) wet season (May to October) rainfall's interannual variability has been examined with emphasis on the rainfall zones of Guinea Coast (GC), Western Sudano Sahel (WSS) and East-ern Sudano Sahel (ESS) in wet and dry years. Rainfall observations from Cli-mate Research Unit (CRU) and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP), and atmospheric circulation fields from National Center for Environmental Prediction (NCEP) were evaluated from 1979 to 2014. The objectives are to evaluate the trends across the zones and their linear relationship with the identified oceanic pulsations, as well as ex-amine the evolution of the anomalous atmospheric circulation associated with the wet and dry years during the wet season months. The results show re-markable variability across the rainfall zones. The areal averaged rainfall anomalies show significant correlation values of −0.2 with Ocean Nino Index (ONI) only on WSS and ESS respectively, whereas with South Atlantic Ocean Dipole Index (SAODI) it shows significant correlation value of 0.3 only on GC, at 95% Confidence Level from a t-test. The analysis of trends in spatial and temporal patterns of the atmospheric circulation fields has extensively presented attributes associated with the wet seasonal rainfall anomalies in the wet and dry years. FGOALS-s2 model showed an outstanding simulation of the spatial and temporal patterns of these attributes, with the discrepancies noted, hence presenting itself as a viable tool in the prediction of seasonal rainfall extremes over West Africa.