The Impact of Kelvin Wave Activity during Dry and Wet African Summer Rainfall Years

Ademe Mekonnen,Carl J. Schreck,Bantwale D. Enyew

doi:10.3390/atmos11060568

Abstract

This study highlights the influence of convectively coupled Kelvin wave (KW) activity on deep convection and African easterly waves (AEWs) over North Africa during dry and wet boreal summer rainfall years. Composite analysis based on 25 years of rainfall, satellite observed cold cloud temperature, and reanalysis data sets show that KWs are more frequent and stronger in dry Central African years compared with wet years. Deep convection associated with KWs is slightly more amplified in dry years compared with wet years. Further, KW activity over North Africa strengthens the lower level zonal flow and deepens the zonal moisture flux in dry years compared with wet years. Results also show that enhanced KW convection is in phase with above-average AEW variance in dry years. However, enhanced KW convection is out-of-phase with average AEW activity in wet years. In general, this study suggests that KW passage over Africa enhances convective activity and more strongly modulates the monsoon flow and moisture flux during the dry years than wet years.

Highlights

It is well documented that synoptic-scale convectively coupled Kelvin waves (KWs) and easterly waves have important influences on the variability of deep convection and low-level flow in the global tropics
As shown above, and as implied in Mekonnen et al [2], we argue that KWs have a different level of influence on African easterly waves (AEWs) initiation and westward propagation in dry versus wet years
This study has highlighted the influence of Kelvin wave (KW) activity on deep convection and African easterly waves (AEWs) over North Africa during the July to September season by separating dry and wet rainfall years

Summary

Introduction

It is well documented that synoptic-scale convectively coupled Kelvin waves (KWs) and easterly waves have important influences on the variability of deep convection and low-level flow in the global tropics. African easterly waves (AEWs) contribute 25–35% to the total convective variability over North Africa and more than 40% the over eastern Atlantic [6]. If one focuses on synoptic scale (2–20 day) variability alone, KWs contribute 10–25% and AEWs contribute 35–50% of the July to September synoptic-scale variability over the peak rainfall areas in West Africa (not shown).

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Methods

Conclusion