Short CommunicationShort-term variability in alongshore winds and temperature off Swakopmund, Namibia, during a non-upwelling event in 1998–1999

Abstract

Swakopmund is a popular coastal resort in Namibia, especially during the summer holiday season when daily sea temperatures can fluctuate several degrees in a short period. Hourly measurements of the near bottom water temperature were collected off the Swakopmund Jetty to investigate the thermal variability in relation to local winds. The thermal regime of this coastal region appears to be controlled by the locally forced Ekman offshore transport. Related changes in offshore transport led those of the surf-zone temperature by about one day. A transfer of kinetic energy from the alongshore wind into the temperature field of the nearshore zone dominated relative short time scales (hourly). The longer periods (7–9 days) are associated with the forcing of poleward-directed continental shelf waves. The origin of the 24–25 day frequencies is not clearly understood. However, it characterises the nearshore wind field as well as the water temperature of the surf zone. These relatively long quasi-cycles could originate from rhythmic changes in the regional wind field as a result of changes in the thermal contrast between sea and land areas.

Keywords: coastal upwelling; Ekman offshore transport; nearshore zone; subinertial waves; Swakopmund; temperature fluctuations

African Journal of Marine Science 2007, 29(1): 141–145