A study of macrophysical and microphysical properties of warm clouds over the Northern Hemisphere using CloudSat/CALIPSO data

This study investigates the general macrophysical and microphysical properties of single-layer warm clouds over the Northern Hemisphere using standard CloudSat products during 2008. The yearly averaged occurrence frequency of single-layer warm clouds is 20.9% over oceans and 9.5% over land, respectively. The cloud top heights over land in different latitude zones exhibit a broader spectral width and more frequent occurrence of strong cloud systems in tropics than that over higher latitudes. The maximum values of liquid water content over land are approximately 10-30% smaller but the occurring altitudes are about 0.5 km higher than those over oceans with the same liquid water path (LWP). The reflectivity profiles clearly demonstrate the growth processes of cloud particles and how these processes vary with increasing LWP. The evolutions of reflectivity over land show a frequency shift toward weaker dBZ values relative to that over oceans with the same LWP, suggesting that high aerosol concentrations may induce suppressed drizzle and delayed precipitation in warm clouds. Additionally, there exists a significant difference between warm clouds formation at the initial stage over ocean and land areas. When LWP is 0.1-0.2 kg m(-2) and optical depth exceeds 25, the dBZ values over oceans increase rapidly downward with increasing optical depth (decreasing height). The faster growth may be caused by the evaporation-condensation mechanism. Over land, however, large droplets are unlikely to appear in the early stage possibly because continental aerosols prevent the evaporation-condensation mechanism to occur, resulting in partially delayed drizzle formation.