Links between the Antarctic Oscillation and winter rainfall over western South Africa

Abstract

Relationships between the Antarctic Oscillation (AAO) and winter rainfall over western South Africa are investigated. This region receives most of its annual rainfall during austral winter and often experiences severe drought. It is found that 6 (6) of the 7 (8) wettest (driest) winters (JJA) during 1948–2004 occur during negative (positive) AAO phase, i.e., positive (negative) pressure anomalies over Antarctica and negative (positive) anomalies over the midlatitudes. The mechanisms by which the AAO appears to influence winter rainfall involve shifts in the subtropical jet, and changes in the low‐level moisture flux upstream over the South Atlantic and in the mid‐level uplift, low‐level convergence and relative vorticity over the region. The anomalous circulation patterns extend into spring; thus, the springs following the identified winters also show similar rainfall anomalies.