Decadal variability of summer Southern African rainfall

By Dieppois, B., Pohl, B., Rouault, M., New, M., Keenlyside, N. and Lawler, D. • 2015

Abstract

Summer Southern African rainfall 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 different for each timescale. Interdecadal fluctuations in summer rainfallI are associated with the Pacific Decadal Oscillation (PDO), while quasi-decadal and interannual fluctuations are related to decadal ENSO-like, often described as the Interdecadal Pacific Oscillation (IPO), and ENSO. Annular geopotential anomalies related the Pacific SST influence strongly interact with those driven by the Southern Annular Mode (SAM). Shifts in the westerlies thus lead to anomalous low-level easterly moisture fluxes from the Mascarene region even though decadal timescales, which are not significantly expressed in the SAM.

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