Relationships between Antarctic sea-ice and South African winter rainfall

Abstract

Evidence is presented of a statistical relationship between anomalies in winter sea-ice over the South Atlantic sector of the Antarctic and winter rainfall over western South Africa. A positive (negative) correlation exists between sea-ice concentration over the Weddell Sea/Drake Passage region (east of the Weddell Sea from 0 to 30°E) and rainfall between May and September. When broken down into early, mid and late winter, the relationships appear stronger for early (May to July) and mid (June to August) winter than for late (July to September) winter and the month of July. In all cases, the relationships occur at 1 to 2 mo lead, suggesting that some predictability of winter rainfall may exist based on sea-ice concentration found earlier in the season. Analysis of circulation patterns associated with anomalously wet and dry winters from 1982 to 2004 indicates that the former are characterised by a cyclonic anomaly over southern South Africa that stretches southwest over the mid-latitude South Atlantic. In addition, there are increases in low level westerly moisture flux, and enhanced uplift, relative cyclonic vorticity and convergence over and upstream of the region. These patterns, combined with evidence of a northward shifted and more intense subtropical jet, indicate that the mid-latitude storm track is located anomalously far north during wet winters and that the cold fronts, which climatologically bring most of the annual rainfall, are likely to intensify just upstream of southwestern South Africa. KEY WORDS: South African Climate · Antarctic sea-ice Resale or republication not permitted without written consent of the publisherClim Res 33: [183][184][185][186][187][188][189][190][191][192][193] 2007 cumpolar Current and atmospheric westerlies, facilitates interaction between atmospheric and oceanic circulation in the mid to high latitudes (White & Peterson 1996, Reason 2000, Renwick 2002 as well as the transmission of mid-latitude climate anomalies around the hemisphere. The most obvious example of the latter is the Antarctic Circumpolar Wave (White & Peterson 1996). As yet, no clear evidence of the influence of this phenomenon on South African climate has been found; however, there are indications that it affects the climate of Gough and Marion Islands located near 40°S and 48°S in the southeast Atlantic and southwest Indian Oceans respectively (Melice et al. 2005).In terms of seasonal variability, most calculations of sea-ice extent vary from a minimum of 3 to 5 million km 2 in February to a maximum of 17 to 20 million km 2 in September (Peixoto & Oort 1992, Wadhams 1994, Godfred-Spenning & Simmonds 1996, Eicken & Lemke 2001. However, the lack of reliable long-term data for Antarctic sea-ice is problematic for studies of Southern Hemisphere climate variability. Satellite data available since the late 1970s has resulted in increased observations and coverage of remote areas in the Southern Hemisphere. Other Antarctic sea-ice data sets that extend back before the 1970s are based on other sourc...

Late Pleistocene records of speleothem stable isotopic compositions from Pinnacle Point on the South African south coast

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High‐latitude forcing of regional aridification along the subtropical west coast of South America

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Spatio‐temporal patterns of rainfall trends and the 2015–2017 drought over the winter rainfall region of South Africa

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