AN AIRCRAFT OBSERVED THERMAL INTERNAL BOUNDARY LAYER ALONG THE CAPE SOUTH COAST

Abstract

Aircraft observations offer a unique meteorological perspective of coastal internal boundary layers along the Cape south coast. One case study near the Gourits River mouth on 22 June 1989 is analysed using aircraft-derived wind, temperature and turbulence data collected every 800 m over a 25 km cross section. A weak coastal low pressure cell imposed a shallow easterly flow and weather conditions were stable and humid. The speed of surface easterly winds halved from the coast to the river under the influence of surface friction. Surface temperatures, measured by an infrared sensor, increased from ITC at the sea to 250C over the River valley. Upward sensible heat fluxes caused a westward tilted thermal internal boundary layer in the first 100 m. Convergence and river channelling forced the thermal internal boundary layer to become vertically aligned above 100 m. Vertical velocity fluctuations were more vigourous in the internal boundary layer. Implications for the dispersion of air pollutants from proposed petroleum refineries and nuclear power stations ate discussed.