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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.
Highlights
The global climate is changing and the population of West Africa (WA), with about 65% of it dwelling in rural areas, mostly depends on rain-fed agriculture for their livelihood [1] [2] [3]
These circulations are typically characterized by the low-level southwesterly monsoon flow, the African Easterly Jet (AEJ) in the middle troposphere between 600 - 650 hPa that is closely linked with the African Easterly Waves (AEW) and the Mesoscale Convective Systems (MCS), and the Tropical Easterly Jet (TEJ) occurring at the upper levels around 150 hPa [6]-[14]
From the foregoing, this study has shown that the recent rainfall variability indexes over WA indicate increments in the rate of West African Monsoon (WAM) wet season (May to October) rainfall at the three zones
Summary
The global climate is changing and the population of West Africa (WA), with about 65% of it dwelling in rural areas, mostly depends on rain-fed agriculture for their livelihood [1] [2] [3]. The WAM is associated with tropical seasonal reversals in both atmospheric circulation and the associated rainfall These circulations are typically characterized by the low-level southwesterly monsoon flow, the African Easterly Jet (AEJ) in the middle troposphere between 600 - 650 hPa that is closely linked with the African Easterly Waves (AEW) and the Mesoscale Convective Systems (MCS), and the Tropical Easterly Jet (TEJ) occurring at the upper levels around 150 hPa [6]-[14]. The roles of the African Westerly Jet (AWJ) over the continent and the West African Westerly Jet (WAWJ) over the Atlantic have been established recently [21] These seasonal reversals are influenced by the Inter-Tropical Convergence Zone (ITCZ) or the Inter-Tropical Discontinuity (ITD), as it shifts northwards with the wet tropical maritime air mass (causing the rainy season) from a quasi-stationary location at 5 ̊N to another quasi-stationary location at 10 ̊N and recedes southward with the dry tropical continental air mass (causing the dry seasons) [22] [23]. Interest of most scientists has been drawn to the variability of the associated WAM rainfall since the severe drought over the region between the 1970’s and 80’s [24]-[29] with emphasis being on its inhomogeneity, noting its high temporal and spatial variability [30]
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