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

Climate Research

Chris J. C. Reason¹  Celia Cook¹  Bruce C. Hewitson¹ 

关键词: South African summer rainfall;    Moisture transport;    Rainfall variability;    Interannual climate variability;    Extreme events;   

DOI  :  10.3354/cr026017

来源: Inter-Research Science Publishing

【 摘 要 】

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. Alink 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. Cyclonicfeatures 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 theeast 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 sourcefor 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 southeasternAfrica. 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.

【 授权许可】

Unknown