Regional airflow over the southern Drakensberg mountains of South Africa

The influence of topography on the airflow, over the southern Drakensberg m ountains of South Africa is examined as part of the Ben Macdhui High altitu de Aerosol and Trace gas Transport EXperiment (BHATTEX). Given the high alt itude of the site, the airflow was dominated by the gradient wind. However when light winds were considered, a clear thermo-topographic forcing of loc al winds was evident. Winds with a northern component (downslope) prevailed in the early hours of the morning, whereas southern component winds (upslo pe) blew predominantly during the afternoon hours. Pilot balloon ascents re vealed the frequent presence of sub-stable-layer jets as air descended over the Drakensberg mountains. Lee eddies also formed.