Interannual to Interdecadal variability of winter and summer southern African rainfall, and their teleconnections.

This study examines for the first time the changing characteristics of summer and winter southern African rainfall, and their teleconnections with large-scale climate through the dominant timescales of variability. As determined by wavelet analysis, the austral summer and winter rainfall indices exhibit three significant timescales of variability over the 20th century: interdecadal (15–28 year), quasi-decadal (8–13 year) and interannual (2–8 year). Teleconnections with global sea-surface temperature and atmospheric circulation anomalies are established here, but are different for each timescale. Tropical/subtropical teleconnections emerge as the main driver of austral summer rainfall variability. Thus, shifts in the Walker circulation are linked to the El Niño Southern Oscillation (ENSO) and, at decadal timescales, to decadal ENSO-like patterns related to the Pacific Decadal Oscillation and the Interdecadal Pacific Oscillation. These global changes in the upper-zonal circulation interact with asymmetric ocean-atmospheric conditions between the South Atlantic and South Indian Oceans; together these lead to shift in the South Indian Convergence 37 Zone, and a modulation of the development of convective rain bearing systems over southern Africa in summer. Such regional changes, embedded in quasi-annular geopotential patterns, consist of easterly moisture fluxes from the South Indian High, which dominate southerly moisture fluxes from the South Atlantic High. Austral winter rainfall variability is more influenced by mid-latitude atmospheric variability, in particular the Southern Annular Mode. The rainfall changes in the southwestern regions of southern Africa are determined by asymmetrical changes in the mid44 latitude westerlies between the Atlantic and Indian Oceans.