Evolution of the 2002-2004 drought over northern South Africa and potential forcing mechanisms
Journal Article
2005
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Authors
Journal Title
South African Journal of Science
Journal ISSN
Volume Title
Publisher
Academy of Science of South Africa (ASSAf)
Publisher
University of Cape Town
Department
Faculty
Series
Abstract
We consider the evolution of the 2003/04 summer drought over
northern South Africa to wetter than average conditions by the end
of the season. This season was neutral (that is, it did not coincide
with either an El Niño or a La Niña event) and yet recorded wellbelow-average
rainfall for at least the first four months of the
summer (October–January) with a transition to above-average rainfall
by March. Previous work investigating other neutral summers
with significantly below-average rainfall over the region (1951/52,
1967/68, 1981/82) have indicated that, in contrast to El Niño dry
summers, there are mid-latitude circulation anomalies south and
southwest of South Africa that lead to an increase (decrease) in the
advection of cool, dry (warm, moist) South Atlantic (South Indian)
air masses over South Africa and hence dry conditions. It is shown
that a similar situation occurred in October–December 2003 but
these circulation anomalies started to break down in January 2004,
resulting in a transition towards above average rainfall by the end of
summer. Although the basic mechanism (modulated air mass
advection) behind the early summer drought is clear, the midlatitude
circulation anomalies that lead to this situation for each significantly
dry neutral summer (1951/52, 1967/68, 1981/82, 2003/04)
are somewhat different. As a result, early identification of these
patterns and potential forecasting of dry conditions prior to the start
of summer is difficult.
Description
Reference:
Reason, C. J. C., & Phaladi, R. F. (2005). Evolution of the 2002-2004 drought over northern South Africa and potential forcing mechanisms. South African Journal of Science, 101(11 & 12), p-544.