The southern oscillation and South African summer rainfall

Abstract

Using data since 1882 the relationship between summer rainfall over South Africa and the ENSO phenomenon is investigated. A strong association between Warm Events and dry spells, and between Cold Events and wet spells is discussed. The temporal and spatial variability in the relationship is presented. Rainfall during December and March correlates significantly with the previous winter's SO1 but rainfall during the mid-summer months, January and February, shows much weaker correlation. A significant relationship is detected between the summer rainfall and mean monthly geopotentials as well as the 850-500 hPa thermal wind over the central parts of South Africa. Distinctions are made between the dominant rain-producing systems with regard to these parameters. During January and February, when the SO/rainfall relationship is fairly weak, rainfall develops in a predominantly quasi-barotropic circulation. On the other hand, during December and March the most significant SO/rainfall correlation coincides with a shift to baroclinic systems. Analysis suggests that a clear signal of the SO can be observed in the phase and amplitude of summertime synoptic-scale baroclinic systems over the South African region.

Long‐range predictability of Zimbabwe summer rainfall

“…From the GCM, the leading empirical orthogonal function of Indian Ocean SSTs accounts for 39% of the total variance in NDJ rainfall in southern Africa. The seasonal changes in predictability appear to be consistent with the findings of Lindesay (1988) andvan Heerden et al (1988) for South Africa. ENSO-rainfall relationships for South Africa are stronger during December to March than the early part of the rainy season.…”

Rainfall trends in the KwaZulu‐Natal Drakensberg region of South Africa during the twentieth century

“…The influence of ENSO events is strongest during the summer rainfall months of December to March when the El Niño/La Niña events have reached maturity (Mason and Jury, 1997). Van Heerden et al (1988) found a strong relationship between summer monthly SOI values and corresponding summer monthly rainfall in South Africa. These findings make it likely that there exists a simultaneous, non-lagged relationship between the ENSO and rainfall in Southern Africa (Hydén and Sekoli, 2000).…”

“…(e.g. Lindesay et al, 1986;Lindesay, 1988;Van Heerden et al, 1988;Jury et al, 1994;Mason, 2001) and that ENSO warm events [negative values of the Southern Oscillation Index (SOI)] are frequently associated with less than average rainfall and drought over much of southern Africa (e.g. Tyson, 1986;Ropelewski and Halpert, 1987;Janowiak, 1988;Van Heerden et al, 1988;Mason and Jury, 1997).…”

Relationships between Rainfall over Semi-Arid Southern Africa, Geopotential Heights, and Sea Surface Temperatures

“…In particular, much attention has been focused on the ENSO-rainfall relationship over the domain of South Africa (Dyer, 1979;Lindesay, 1986Lindesay, , 1988Harrison, 1986;Van Heerden et al, 1988;Matarira, 1990;Lindesay and Vogel, 1990;Walker, 1990;Mason and Lindesay, 1993;Jury et al, 194J4). It was found that the Southern Oscillation Index (SOT) indicates a positive simultaneous correlation with 1996, Meteorological Society of Japan rainfall during the southern summer months, while the strongest correlations are found during December and January (Lindesay, 1988).…”

“…It should be noted that the ENSOSouth African rainfall association is modulated with the phase of the Quasi-Biennial Oscillation (Mason and Lindesay, 1993). The continental circulation pattern linking the warm ENSO event and reduced South African rainfall is characterized by respective positive and negative pressure anomalies almost throughout the troposphere over the southern African subcontinent and regions southward (Wright, 1977;Van Loon and Madden, 1981;Pan and Oort, 1983;Van Loon and Shea, 1985;Lindesay, 1986;Van Heerden et al, 1988;Matarira, 1990). That is, an enhanced poleward pressure gradient.…”