Wet and dry spells within particularly wet and dry summers in the South African summer rainfall region

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 26:17-31 (2004) - doi:10.3354/cr026017 Wet and dry spells within particularly wet and dry summers in the South African summer rainfall region Celia Cook1, Chris J. C. Reason2,*, Bruce C. Hewitson1 1Climate Systems Analysis Group, Department of Environmental and Geographical Science, 2Department of Oceanography, University of Cape Town, Private Bag, Rondebosch 7701, Cape Town, South Africa *Corresponding author. Email: cjr@egs.uct.ac.za ABSTRACT: Atmospheric moisture transport over southern Africa and surrounding oceans is considered during wet and dry conditions over the South African summer rainfall region. Wet and dry synoptic spells within wet and dry austral summers are examined. A link between synoptic and seasonal timescales is investigated using seasonal statistics of wet and dry spells. Dry synoptic spells exhibit divergent moisture flux over South Africa, with inflow from the mid-latitude ocean regions to the south. Cyclonic features off the east coast may exist and attract moisture away from South Africa. For wet synoptic spells, there tends to be increased moisture flux from the tropical or subtropical southwest Indian Ocean (SWIO), either associated with ridging along the east coast or a deep low over the interior. Seasonal modulations of the intensity of the heat low over Angola/Namibia appear important for influencing early (OND) and late (JFM) summer rainfall over South Africa. This low may act as the tropical source for tropical temperate troughs and their associated cloudbands that are major synoptic rain-producing systems. Wet (dry) summers are often associated with a southward (northward) shift and strengthening (weakening) of the ITCZ over tropical southeastern Africa. Seasonal rainfall is found to be related to the distribution of wet and dry spells within the season, such that wetter seasons tend to have longer or more intense wet spells rather than a greater number of wet spells. KEY WORDS: South African summer rainfall · Moisture transport · Rainfall variability · Interannual climate variability · Extreme events Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 26, No. 1. Online publication date: April 19, 2004 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2004 Inter-Research.