Abstract. Monsoonal rainfall is the primary source of surface water in India. Using 12 years of in-situ and satellite observations, we examined association of aerosol loading with cloud fraction, cloud top pressure, cloud top temperature, and daily surface rainfall over Indian summer monsoon region (ISMR). The analyses showed positive correlations between aerosol loading and cloud properties as well as rainfall. A decrease in outgoing longwave radiation and increase in reflected shortwave radiation at the top of the atmosphere with an increase in aerosol loading further supported a seminal role of aerosols on cloud systems. Significant perturbation in liquid- and ice-phase microphysics was also evident over ISMR. For the polluted cases, delay in the onset of collision-coalescence processes and enhancement in the condensation efficiency, allows for more condensate mass to be lifted up to the mixed-colder phases. This results in the higher mass concentration of bigger sized ice-phase hydrometeors and, therefore, implies that the delayed rain processes eventually lead to more surface rainfall. Numerical simulation of a typical rainfall event case over ISMR using spectral bin microphysical scheme coupled with Weather Research Forecasting (WRF-SBM) model was also performed. Simulated microphysics also illustrated the initial suppression of warm rain coupled with increase in updraft velocity under high aerosol loading leads to enhanced super-cooled liquid droplets above freezing level and ice-phase hydrometeors, resulting in increased accumulated surface rainfall. Thus, both observational and numerical analysis suggest that high aerosol loading may induce cloud invigoration and thereby increasing surface rainfall over the ISMR. While the meteorological variability influence the strength of the observed positive associations, our results suggest that the persistent aerosol-associated deepening of cloud systems and intensification of surface rain amounts was applicable to all the meteorological sub-regimes over the ISMR. Hence, we believe that these results provide a step forward in our ability to address aerosol-cloud-rainfall associations based on satellite observations over ISMR.
Sensitivity of speleothem records in the Indian Summer Monsoon region to dry season infiltration
