Tropical-temperate links in southern African and Southwest Indian Ocean satellite-derived daily rainfall

An objective analysis of daily austral summer rainfall variability in the southern Africa and Southwest Indian Ocean region, using satellite-derived rainfall estimates, is conducted for the first time. A new method to reconstruct the GOES Precipitation Index (GPI), at the daily scale on a 2.5 degrees grid, from ISCCP D1 satellite products is introduced. Estimates using this method are validated with GPI estimates on a monthly scale over global and regional domains. The reconstructed GPI (RGPI) estimates correlate very strongly with those from the GPI. Empirical Orthogonal Function (EOF) analysis of RGPI daily rainfall estimates for November-March (15-40 degrees S, 10-70 degrees E) shows that the leading mode of variability is characterised by tropical-temperate links in all months. These rain bands are orientated from north-west to south-east across the study region. Events characteristic of the leading mode of variability are relatively infrequent, occurring on average only twice per month, and can be stationary or propagating systems. A rainfall dipole exists, with parallel centres of activity producing enhanced (suppressed) activity over the Southwest Indian Ocean, associated with suppressed (enhanced) activity over southern Africa. Previous studies have shown that this dipole exists at monthly and interannual scales. This rainfall dipole has tropical-temperate links, whereas previous land-based rainfall analyses have emphasised only the tropical and subtropical components. Copyright (C) 1999 Royal Meteorological Society.