Bimodal peak in mid-level tropical layer clouds observed by CloudSat

Distribution plots of tropical (30°S-30°N) cloud top heights versus cloud mean thickness reveal two distinct populations of mid-level layer clouds; a low peak at 5-6 km and an upper peak at 7-8 km. ‘Layer' is an appropriate adjective as the clouds are generally thin (mean thickness < 2 km) with low reflectivity (dbz < 0). This study examines the two peaks spatially and seasonally using 2D histograms for over a full year of CloudSat data (15 June 2006 to 28 August 2007). Contoured frequency by altitude diagrams (CFADs) are used to understand the reflectivity of the upper and lower peaks. Total column cloudiness in the presence of the layer clouds is also shown by documenting overlapping cloud amounts. Both peaks are found throughout the Tropics (but with different latitudinal and seasonal dependence). Comparison of the two peaks will also be studied using ECMWF data that is concurrent with CloudSat, as well as OLR data.