Abstract
AbstractAn 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.
Highlights
Short-to-medium-range convective rainfall variability has a direct influence on rain-fed agricultural productivity because it determines the amount of available soil moisture (e.g., Black et al, 2016) as well as the frequency of replenishing surface and underground water for production (Taylor et al, 2019)
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)
This study aims at advancing knowledge of the synoptic-scale interaction between WEA and EEA in the context of daily precipitation anomalies, which are more linked to convective processes and more relevant to human impacts than OLR
Summary
Short-to-medium-range convective rainfall variability has a direct influence on rain-fed agricultural productivity because it determines the amount of available soil moisture (e.g., Black et al, 2016) as well as the frequency of replenishing surface and underground water for production (Taylor et al, 2019). Sinclaire et al (2015) noted that during March–June, eastward propagating CCKWs favour initiation of synoptic-scale convective systems and that annually, an average of six to seven CCKWs propagate through the Congo basin in this period While all these studies used OLR to identify CCKWs, we take a unique approach of identifying the CCKWs, using a novel dynamics-based equatorial wave dataset. Mekonnen and Thorncroft (2016) found a dipole pattern of synoptic-scale convective activity between the Congo Basin and Eastern Africa They observed that CCKWs modulate a coherent eastward/northeastward propagating convective signal, that oscillates between enhanced and suppressed states with a periodicity of 3– 4 days. This dataset is available from 1997–2018, this study uses the daily averaged data for the period 1998–2013
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