The influence of the MJO on Spring Equatorial West African convection

This paper characterizes the influence of the Madden-Julian Oscillation (MJO) on spring rainy season (March-June) convection variability over Equatorial West Africa (EWA) and investigates mechanisms of association. It is found that the MJO has a significant impact on convection anomalies over the region. This impact is primarily due to the direct influence of the eastward movement of the MJO convective core into EWA, which is associated with westerly low-level wind anomalies that advect moisture from the Atlantic Ocean to the region, and to MJO-associated SST anomalies over the Gulf of Guinea, which modulate precipitation anomalies over large parts of the region. In addition, equatorial Rossby and Kelvin waves triggered by MJO convection anomalies over the Indian Ocean have a significant and systematic influence on EWA spring season precipitation, though their impact is smaller than the direct influence of the MJO convective core. The Kelvin wave contribution and the relative strength of the direct MJO convective influence compared to that of equatorial wave activity differs from findings of studies that have examined MJO influence on EWA during boreal summer. Importantly, in the spring season the influences of MJO convection and each of the MJO-associated convectively coupled equatorial waves coincide, reaching EWA approximately twenty days after MJO convection initiates in the Indian Ocean. This coincident timing enhances the total MJO impact on the region, and it also implies that MJO events have potential for prediction of regional-scale convection and rainfall anomalies over EWA in this season.

Key words: Madden-Julian Oscillation, West Africa, intraseasonal variability, Equatorial West Africa