Aerosol-heavy precipitation relationship within monsoonal regimes in the Western Himalayas

Abstract

Studies reported increased heavy precipitation and aerosol loading in Western Himalayas (WH) due to changes in large-scale dynamics and anthropogenic emissions. In this study, we investigate the long-term relationship between aerosols and heavy precipitation from 2001 to 2020 by incorporating the changes in dynamics and eliminating the influence of meteorological covariates. We analyzed composites of aerosol optical depth (AOD) from MERRA2 reanalysis and precipitation from GPM IMERG products within monsoonal regimes – M1 (westerly), M2 (westerly + easterly) and M3 (easterly) with distinct large-scale dynamics. A significant positive correlation is found between aerosols and heavy precipitation in M1 (0.27) and M2 (0.15) but not M3. We eliminated the influence of three covariates, specifically the moisture flux convergence (MFC), Webster Yang Index (WYI), and relative humidity (RH) at 850 hPa, on the aerosol-heavy precipitation relationship. We found MFC to be the strongest influencer using partial correlation analysis, whereas WYI and RH only weakly affected this relationship. The overall partial correlation coefficient between aerosols and heavy precipitation is 0.17 in both M1 and M2 but insignificant in M3. Further, we studied the evolution of cloud properties during heavy precipitation under distinct dynamics. We found smaller cloud droplets with a narrow size distribution in M1, but larger droplets and broad distribution for M3. We did not find a significant correlation between AOD and cloud properties in the ice phase in any of the regimes. Our findings imply that dynamical changes result in distinct aerosol-heavy precipitation relations and microphysical processes causing heavy precipitation.