Variability of summer rainfall over Madagascar: Climatic determinants at interannual scales

Variability of convective rainfall in the austral summer season over central Madagascar is studied using an area‐rainfall index, local radiosonde data, and gridded information on outgoing longwave radiation (OLR), sea‐surface temperature, and tropospheric winds. Seasonal rainfall patterns are influenced by topography, monsoon and trade wind circulations, and tropical cyclone events. The Inter Tropical Convergence Zone overlies the north‐west coast, where summer rainfall averages 47 cm month−1. Climatic conditions that affect convective rainfall at interannual time‐scales are studied through spatial lag correlation analysis. Sea‐surface temperature is weakly correlated with rainfall departures, with positive values in the central Indian Ocean reaching +0.41 at lags −4 and 0 months. Strongest positive correlations (+0.45) gradually shift to the central South Atlantic Ocean at lag 0 and +2 months. Wind correlations imply that increased upper level tropical easterly flow overlying enhanced low‐level north‐west monsoon flow favours above normal rainfall. Regional teleconnection patterns identified by rainfall‐OLR correlations are remarkably similar to those for Quasi‐biennial oscillation (QBO)‐OLR correlations, suggesting that up to one‐third of the interannual convective variance can be explained by the phase of the QBO. Copyright © 1995 John Wiley & Sons, Ltd