Abstract
Principal components analysis of satellite outgoing longwave radiation (OLR) anomalies over southern Africa forms the basis of this work. OLR anomalies, which are closely correlated with rainfall anomalies and vegetation cover, are formulated for early and late summer, the season when convective clouds develop over southern Africa. The first four principal component modes account for 82 to 85% of the total inter-annual convective variability in the period 1975–1994. The dominant terrestrial modes take the form of truncated dipoles (36%). NW-SE oriented loading patterns contributed by cloud bands and poleward tropical outflows, form the second most important climate mode (25%). Lower order modes are dominated by monsoon effects (12%) and isolated cells (10%). The dominant modes of convective variability appear related to the phase of the Southern Oscillation and its regional signals. The principal component results indicate that attention should be given to understanding mechanisms underlying dipole circulation systems.
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