Spatial and diurnal variability in the Saharan Boundary Layer during GERBILS (2007)

The Saharan boundary layer has an important influence on the structure and composition of the atmosphere at regional scales and above. The thermodynamic structure of the boundary layer will determine the influence of the heat low on regional circulations in West Africa. The dynamics in the Saharan boundary layer determine the lofting of mineral dust and thus influence long-range transport across the Atlantic ocean.

The United Kingdom Meteorological Office organised the GERBIL (GERB Intercomparison of Longwave and Shortwave Radiation) campaign from 18-29 June 2007. Eight transects were conducted with the FAAM BAE146 aircraft across the Southwestern Sahara from bases at Niamey and Nouakchott. Observations were obtained with dropsondes as well as of aerosol, radiation, and standard meteorological variables during low-level boundary layer flights. Operational forecasts were made during the campaign using the COSMO model of the Deutscher Wetterdienst run twice daily at the University of Karlsruhe Scientific Supercomputing Center with 7 km horizontal resolution and 35 levels.

In this presentation we explore the spatial and diurnal variability of the boundary layer in the Saharan region during the GERBILS campaign through a combined analysis of observations and model output. We relate this variability to synoptic scale features such as the heat low, the inter-tropical discontinuity, the low-level monsoon flow, African easterly waves, and nocturnal moist low-level onshore flow across the west coasts of Mauritania and Senegal. The impact of these subsystems on the heat and water budget in the Saharan/Sahelian region is estimated using budget calculations.