Wind-driven upwelling off the Namaqualand coast of South Africa in spring 1980

Abstract

Sea surface temperature was monitored off the Namaqualand coast of South Africa (29–32°S, 16–18°E) during the spring of 1980 by aerial radiation thermometry. The aircraft flew a grid pattern extending 30 km inland and about 100 km offshore. Wind data were obtained from aircraft drift measurements at 152 m above sea or local ground level. A time series of wind information from a coastal station in the centre of the study area showed a longshore wind direction (170°) with a slight onshore component due to the prevalence of seabreezes. The South Atlantic high-pressure cell and equatorward wind flow became established during October 1980. However, in November a persistent upper-air trough caused wind reversals affecting the distribution of sea surface temperature. Upwelling off Namaqualand is typically confined to the coastal strip, but with a broad plume of cold water extending offshore near 30°S. The location of the minima in sea surface temperature is attributed to the proximity of a southerly wind maximum and to an equatorward broadening of the continental shelf. Three cases are presented to describe the pattern of upwelling off Namaqualand under a varying history of winds. © 1986 Taylor & Francis Group, LLC.