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 Eastern Sudano Sahel (ESS) in wet and dry years. Rainfall observations from Climate 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 examine the evolution of the anomalous atmospheric circulation associated with the wet and dry years during the wet season months. The results show remarkable 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.

Variability and trends of atmospheric moisture in recent West African monsoon season and the Coordinated Regional Downscaling Experiment‐Africa projected 21st century scenarios

“…Several studies have examined the recovery from the droughts of the 1970s and 1980s over West Africa (WA) (Hagos and Cook, ; Nicholson, ; Sanogo et al ., ; Okoro et al ., ). However, the roles and magnitudes of the related mechanisms such as the fluctuations in aerosols, atmospheric and soil moisture gradients, vegetation, baroclinic and barotropic instability and sea surface temperature in the recovery are not fully understood (see Zheng and Eltahir, ; Grist and Nicholson, ; Dai et al ., ; Vizy and Cook, ; Gaetani et al ., ; Nicholson et al ., ).…”

Assessing the Skill and Reliability of Seasonal Climate Forecasts in Sahelian West Africa

“…In Sahelian West Africa, the variation in year-to-year rains is heavily influenced by the slowly varying components of the climate system, particularly the neighboring oceans and land surface conditions (Rodríguez-Fonseca et al 2015;Druyan and Fulakeza 2018). The onset, duration, cessation and amount of rains is associated with the poleward migration of the West African monsoon (WAM) and affected by the large-scale flow, including changes in the African easterly jet (AEJ), tropical equatorial jet (TEJ), and Saharan heat low (Vellinga et al 2013;Okoro et al 2017). Topography has also been argued to have an important influence on the WAM migration (Sultan and Janicot 2003), as well as inertial instability advancing moisture migration northward (Cook and Vizy 2006).…”