THE MODULATION OF SEA-SURFACE TEMPERATURE AND RAINFALL ASSOCIATIONS OVER SOUTHERN AFRICA WITH SOLAR-ACTIVITY AND THE QUASI-BIENNIAL OSCILLATION

Correlations between solar activity and southern African rainfall, stratified according to the phase of the Quasi-Biennial Oscillation (QBO), reveal significant zero and 3-month lag associations in both the summer and the winter rainfall regions. The solar-rainfall associations are significant for in-season rainfall only when the QBO is in its easterly phase, while for out-of-season rainfall, significant associations are evident when the QBO is in its westerly phase. When the QBO is in its easterly phase, an increase (decrease) in early season solar activity (October-December in the summer rainfall region, April-June in the winter region) produces a synchronous increase (decrease) in rainfall over both the summer and the winter rainfall regions. The same increase (decrease) in solar activity produces a significant decrease (increase) in rainfall over the regions in the second half of the same rainfall season, 3 months later. When the QBO is in its westerly phase, out-of-season changes occur with both the winter precipitation of the summer rainfall region and the summer precipitation of the winter rainfall region, showing a tendency to become somewhat higher (lower) following an increase (decrease) in solar activity. During the early and late summer seasons, when the QBO is in its easterly phase, anomalous rainfall receipts over the summer rainfall region are the result of anomalies in the tropical atmospheric circulation of the region, which can in part be understood by reference to the sea surface temperature departures of the southwest Indian Ocean. In contrast, the rainfall anomalies observed in the southwest Cape Province during its peak rainfall season in winter can be related to anomalies in the temperate atmospheric circulation and sea surface temperature anomalies in the South Atlantic Ocean. Out-of-season associations between solar activity and southern African rainfall are evident for the summer rainfall region when the QBO is in its westerly phase and can be explained by reference to sea surface temperature anomalies in both the South Atlantic and the southwest Indian oceans. The phase of the QBO appears to modulate the association between solar activity and rainfall and also between solar activity and sea surface temperatures.