Diurnal wind cycles and upwelling off the northern portion of the Cape Peninsula in summer

Abstract

Summer winds along the north-west coast of the Cape Peninsula were investigated to determine their impact on a localized upwelling plume. From automatic weather stations, moored buoys and aerial surveys, a pronounced diurnal cycle in south-easterly wind flow was documented. The orography of the northern portion of the Cape Peninsula is complex, with mountain ridges causing a nocturnal downslope wind jet exceeding 10 m·s−1 during anticyclonic weather conditions. This phenomenon is detailed in three case studies presented. When an inversion layer descended below the top of nearby Table Mountain (1 000 m), a downwind wake developed extending 40 km over the Atlantic Ocean. The wake effectively separated surface upwelling plumes emanating from either side of Cape Town, and it expanded and contracted in sympathy with changes in the horizontal temperature gradient and the inversion layer. A wind-shear line developed at the interface between the downslope jet and the wake with a 24-hour cycle. © 1985 Taylor & Francis Group, LLC.