The observed synoptic scale precipitation relationship between Western Equatorial Africa and Eastern Equatorial Africa

An improvement to subseasonal (i.e., days to weeks) rainfall prediction across Equatorial Africa is an important area of current research. This is because most countries in this region are highly dependent on rain-fed agriculture, and so millions of livelihoods are at risk in the event of an unexpected poor harvest. This study examines 16 years of daily precipitation anomalies to investigate the relationship in precipitation between Western Equatorial Africa (WEA) and Eastern Equatorial Africa (EEA). Using lead/lag correlation and spatio-temporal correlation patterns over various sub-regions, a synoptic-scale relationship in precipitation is presented between WEA and EEA, in which precipitation over EEA lags precipitation over WEA by 1-2 days. In addition, central WEA and sub-regions in South Sudan display a synoptic-timescale precipitation contrast, suggesting a weak precipitation dipole. Consistent with the known heterogeneity characteristic of Equatorial Africa's precipitation, our findings suggest that the 1-2 days precipitation relationship is dependent upon the sub-region under investigation. Furthermore, our results indicate a coherent synoptic-timescale eastward/northeastward propagating signal with a speed of approximately 12 m/s. Composite and correlation analyses of precipitation anomalies and a novel equatorial wave dataset show an apparent connection between eastward/northeastward propagating wet anomalies and Kelvin wave lower-tropospheric convergence. This suggests that Convectively Coupled Kelvin Waves (CCKWs) play a role in modulating the 1-2 days convection and precipitation propagation between WEA and EEA. These results imply that monitoring the propagation characteristics of CCKWs may be important in synoptic-timescale forecasting over Equatorial Africa.