Desert dust aerosol columnar properties over ocean and continental Africa from Lidar in-Space Technology Experiment (LITE) and Meteosat synergy

Abstract : The new generation of spaceborne backscatter lidar systems, prefigured by the Lidarin-Space Technology Experiment (LITE) mission in September 1994, will give newinsight on the vertical distribution of both aerosols and clouds in the atmosphere. This isespecially of importance for aerosols over land, where retrievals from passive sensorsare known to be more difficult because of the surface contribution. Here we analyzemineral dust aerosol transport events through a new approach coupling the active LITEand passive Meteosat-5 spaceborne observations. The Meteosat-derived aerosol opticalthickness at 550 nm is shown to be a good boundary condition for the lidar inversion inorder to retrieve both the aerosol backscatter to extinction ratio (BER) and the aerosolextinction vertical profile above the Tropical Atlantic Ocean (TAO) and the MediterraneanSea. Sensitivity tests indicate that the aerosol scattering coefficient is retrieved within a20% relative uncertainty. Air mass trajectories allow us to further retrieve the verticalprofile of aerosol optical properties over the continent in the Saharan Heat Low (SHL)region using the BER determined over the ocean. Results confirm a large dispersion ofthe BER which is not attributed to errors in the method. This shows the need to account forsuch dispersion in the retrieval of dust aerosol optical thickness and aerosol impact onthe earth radiative budget. The coupling between LITE and Meteosat-5 made here isshown to be interesting for an improvement of the direct dust aerosol forcing, and resultsshould be improved by the CALIOP-MODIS synergy.