Aerosol impacts on cloud thermodynamic phase change over East Asia observed with CALIPSO and CloudSat measurements

Impacts of aerosols on subfreezing cloud thermodynamic phase change over East Asia are studied by using 4 year combined CloudSat radar and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar measurements. The mean occurrence frequencies of supercooled-liquid, mixed-phase, and glaciated clouds over East Asia are 10.4%, 10.3%, and 16.9%, respectively. Over northwest of East Asia (32-44°N, 75-100°E), subfreezing clouds are dominated by glaciated clouds with a mean relative cloud fraction (RCF) of ~60% and over southeast (16-32°N, 95-120°E) are dominated by supercooled-liquid clouds with a mean RCF of ~50%. Although cloud top temperature (CTT) differences contribute largely to the thermodynamic phase differences, northwest of East Asia has ~20% larger glaciated (smaller mixed-phase) RCFs than those of southeast at the same CTT. Seasonal anomalies of glaciated and mixed-phase RCFs correlate well with the seasonal variations of dust occurrence frequency. In addition, subfreezing clouds associated with mineral dust contain approximately 5%, 10%, and 20% larger glaciated (smaller mixed-phase) RCFs than those associated with polluted dust, smoke, and background aerosols at any given CTT. It is suggested that dust impacts on subfreezing clouds over East Asia by providing abundant effective ice nuclei to glaciate mixed-phase clouds, although the impacts of large-scale dynamics and water supply mechanisms cannot be ruled out.