Nature and Extent of Shallow Marine Convection in Subtropical Regions: Detection with airborne and spaceborne Lidar-Systems over the tropical North Atlantic Ocean

Abstract. Shallow marine cumulus convection over the Atlantic ocean near Barbados is studied with observations by airborne and spaceborne lidar instruments performed during the field campaign Next-generation Aircraft Remote Sensing for Validation Studies (NARVAL). For the first time airborne lidar measurements with the DLR high spectral resolution lidar system WALES on-board the German research aircraft HALO were conducted over the tropical North Atlantic Ocean. In the course of NARVAL several CALIPSO satellite underflights were performed, which allow comparisons of detected cloud top edges from the two lidar instruments (i.e. WALES and CALIOP on-board CALIPSO). The study concentrates on the comparison and investigation of detected cloud top height distributions derived from measured WALES and CALIOP lidar profiles by use of a newly developed cloud detection algorithm. This allows to test the utilization of satellite based lidar systems for the observation of shallow marine convection. The distribution of cloud top heights during wintertime measurements shows a two-layer structure with maxima in ∼1000 m and ∼2500 m in both WALES and CALIOP measurements. Cloud top heights vary with latitude. The analysed WALES and CALIOP data shows most frequent cloud tops in 10° to 20° N at heights from 1500 to 2500 m. A meridional decrease of detected cloud top heights over the subtropical North Atlantic Ocean, with lower values in the North, is observed. Approximately 36 % of all clouds in the Atlantic trades are detected to have a horizontal extent of less than 1 km in the winter season. Cloud gaps shorter than 1 km dominate the Atlantic trades. They make up approximately 45 % of all detected cloud gaps.