The Influence of the Regional Hadley and Walker Circulations on Precipitation Patterns over Africa in El Niño, La Niña, and Neutral Years

Abstract

This study focuses on the differential impacts of the positive (El Nino), negative (La Nina), and neutral phases of the El Nino Southern Oscillation (ENSO) on precipitation over Africa during DJF and JJA, evaluated through changes in the regional Hadley and Walker Circulations. Identification of the Hadley and Walker Cells was done using stream function mass transport calculations of ERA-Interim reanalysis data from 1979 to 2014. Analysis of the spatial pattern of precipitation anomalies shows that during DJF, El Nino (La Nina) negatively (positively) impacts precipitation over the African continent. During JJA, El Nino (La Nina) influences precipitation variability over the Sahel region, producing positive (negative) anomalies. Negative precipitation anomalies associated with El Nino (DJF) over southern Africa are linked to a strengthening in subsidence of the descending branch of the regional Hadley Cell, and during JJA the negative precipitation anomalies over the Sahel are associated with a weakening of the ascending branch of the regional Hadley Cell. During La Nina events in DJF, there is a tendency toward increased convection in southern Africa, associated with a stronger ascending branch and weaker descending branch of the regional Hadley Cell. During La Nina events in JJA, positive precipitation anomalies over the Sahel are associated with an intensification of the ascending branch of the regional Hadley Cell north of the equator.