OBSERVATIONS OF BOUNDARY-LAYER DEVELOPMENT DURING THE HAPEX-SAHEL INTENSIVE OBSERVATION PERIOD

The radiosonde measurement programme of the boundary layer during the Hydrologic Atmospheric Pilot Experiment in the Sahel (HAPEX-Sahel) is described. Typical examples of boundary layer evolution at two sites f or wet and dry periods are shown. The Central Site was consistently dr yer and warmer than the Southern Site and also reached higher boundary layer depths in the dry period in October. A brief analysis of surfac e flux variability is used to determine the errors associated with usi ng a single average value for boundary layer input. Budget calculation s using a mixed layer model show that advection plays an important rol e in the early morning budgets of heat and moisture. In the dry period subsidence also contributed to boundary layer heating.