The atmospheric modulation of extended wet and dry spells over South Africa, 1958–1978

Abstract

Abstract Differences in annual geopotential heights at the 850 and 500 mb levels between 16 pairs of stations have been submitted to principal component analysis to identify the most important statistically uncorrelated pressure patterns accounting for the variance of the annual pressure field over South Africa and adjacent oceans. By correlating component scores for the period 1958/9 to 1977/8 with annual rainfall an attempt has been made to determine the regional rainfall responses to variations in different circulation types. Regional variations in annual rainfall are shown to be significantly linked to variations in both low latitude forcing, associated with tropical easterly airflow and cyclonic wave perturbations therein, and mid‐latitude forcing, associated with a variety of both cyclonic and anti‐cyclonic perturbations in the westerlies. It has been shown that it is primarily variations in the atmospheric field of motion at the 500 mb level that are responsible for year‐to‐year differences in annual rainfall totals.