Interannual winter rainfall variability in SW South Africa and large scale ocean–atmosphere interactions |
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Authors: | C J C Reason M Rouault J-L Melice D Jagadheesha |
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Institution: | (1) EGS and Oceanography Departments, University of Cape Town, Rondebosch, South Africa, ZA;(2) IRD, Laboratoire d’Oceanographie Dynamique et de Climatologie, UPMC, Paris, France, FR |
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Abstract: | Summary The Southwestern Cape (SWC) region of South Africa is characterized by winter rainfall mainly via cold fronts and by substantial
interannual variability. Evidence is presented that interannual variability in SWC winter rainfall is related to sea-surface
temperature (SST) and sea-ice anomalies in the central South Atlantic and adjoining Southern Ocean and to large scale ocean–atmosphere
interaction in this region. During wet winters, the jet is strengthened just upstream of the SWC and significant cyclonic
anomalies extend from the SW Atlantic over the region. SST tends to be anomalously warm (cool) in the SW Atlantic and SE Atlantic
(central South Atlantic) and sea-ice extent increased in the central South Atlantic sector of the Southern Ocean. These patterns
favor increased cyclogenesis upstream, a more northward track of midlatitude depressions, local intensification near the SWC
and enhanced rainfall. Roughly the reverse patterns occur during dry winters. Some preliminary results from atmospheric GCM
experiments are presented which help support these findings.
Received November 9, 2001 Revised December 28, 2001 |
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