Changes in Multilayered Cloud Structure and Associated Rain Properties in High and Low Aerosol Regimes over South Asian Summer Monsoon Region

Illustrating the greenhouse gas feedback and aerosol impacts responsible for the reported changes in the South Asian summer monsoon pattern is crucial to predict the future climate. Lack of an observation-based precise representation of aerosol-cloud-precipitation interaction in climate models is responsible for the limitation of robust evaluation. Here, we aim to assess the changes in cloud vertical structure and microphysical properties (for water and ice clouds) as a function of rainfall intensity in the South Asian summer monsoon region (latitude -5⁰ - 60⁰ North and 50⁰ - 150⁰ East) for the low (< 25th percentile), high aerosol (>75th percentile) regimes. We include data for cloud microphysical and vertical properties from four years (2007-2010) of active radar measurement (CloudSat). We also incorporate NOAA GPCP daily gridded precipitation data and MODIS Collection-6 aerosol products for the months of June-July-August (JJA season). We observed that the average daily monsoon precipitation is around 4.34 mm in the study area. The Indian Ocean, Bay of Bengal and Southern China experience higher (>10 mm) daily precipitation rate than the average, where, the observed AOD is considerably low (<0.4). The western and central part of India, north of the Himalayan region and Northern regions of China experience smaller (< 4 mm) than average daily precipitation. Here the AOD value is on the higher (>0.7) side. The ice and liquid water path in the study region is highly variable from region to region with mean values of 515.8 g/m² and 70.16 g/m². For the single-layered cloud structures, the mean cloud top height for low aerosol and the high aerosol regime vary from 10.9 km to 12.5 km for ice clouds and 4.5 km to 5.2 km for liquid clouds. The cloud base height for low to high aerosol regime increases from 5.15 km to 6.08 km for ice clouds and 4.5 km to 5.2 km for liquid clouds. These changes point towards possible invigoration of clouds in highly polluted regions. In the case of multi-layered cloud systems, the signature of cloud invigoration is more prominent in the lowest layer than the upper levels. A better representation of aerosol-cloud-precipitation interaction in weather and climate models would facilitate increased forecast confidence for the South Asian summer monsoon region.