Satellite OLR and microwave data as a proxy for summer rainfall over sub‐equatorial Africa and adjacent oceans

Abstract

AbstractThe potential for using satellite outgoing longwave radiation (OLR) and passive microwave data as a proxy for rainfall over sub‐equatorial Africa and adjacent oceans is explored. Correlations between anomalies of field OLR and a summer rainfall index are −0.67 to −0.93 over central southern Africa, where the amplitude of interannual fluctuation in the decade 1975–1984 is largest. OLR‐rainfall correlations decline to −0.42 over Madagascar owing to a less homogeneous distribution of rainfall. Over South Africa during the winter dry season the correlation becomes positive except over the eastern seaboard where sea‐surface temperatures remain high.Satellite microwave estimates of cloud liquid water (LW) over the oceans surrounding southern Africa are presented for selected months during 1988 and 1989. Agreement is found between coastal rainfall and adjacent oceanic LW patterns. Contrasting distributions of interior and coastal rains in January and October 1989, respectively, are associated with the positioning of standing troughs evident in concentrated areas of high LW values in the mid‐latitudes. The advance and structure of the Inter Tropical Convergence Zone (ITCZ) over the tropical South‐west Indian Ocean is illustrated in monthly composites.