Exploring the hidden role of aerosols in altering the Indian Summer Monsoon rainfall variability through cloud modification

In recent years, the scientific community has placed growing emphasis on the impact of aerosols on the Indian Summer Monsoon (ISM) system. The ISM, the world’s strongest monsoon system, delivers approximately 80% of India’s annual rainfall from June to September, sustaining ecosystems, agriculture, and millions of livelihoods. The Indian subcontinent, with its diverse geography, dense population, and industrial zones, is a major source of aerosols through short-range and long-range transportation. Aerosols are instrumental in the process of cloud formation, functioning as cloud condensation nuclei (CCN) and ice nuclei (IN), which are vital for the formation and evolution of cloud hydrometers. Numerous possible mechanisms by how aerosols influence rainfall have been suggested by recent research on the direct radiative effects of aerosols. However, the microphysical impact of aerosols on monsoonal rainfall in the Indian Summer Monsoon Region (ISMR) remains largely unexplored. Indian summer monsoon rainfall is influenced by the large-scale circulation and different monsoon drivers. The large-scale driver modulates clouds and indicates the sign of seasonal mean ISM rainfall anomalies and the role of aerosols are secondary. Our current understanding of both the direction and magnitude of aerosol-cloud interaction (ACI), which induced changes in rainfall is insufficient. Furthermore, changes in thermodynamic and climatic circumstances, precipitation types, their vertical distribution in the atmosphere, cloud and dynamics all have a significant impact on the ACI and give feedback to ISM rainfall. In this context, we will carry out a comprehensive analysis of  multi-satellite observations and numerical model simulations  to examine the role of aerosol on cloud properties and precipitation susceptibility. The analysis of multi-satellite data reveals considerable spatial and vertical variability of dust aerosols over the ISM region. Increased dust activity can modify the monsoon cloud system, leading to significant changes in the microphysics of both the liquid and ice phases over the ISM region. The process analysis of ACI is crucial for accurately predicting monsoonal rainfall and will help resolve discrepancies in aerosol-cloud-rainfall interactions between models and observations. While more aerosols tend to reduce the cloud drop size and delay the warm rain, during the Indian summer monsoon, this is overcome by invigoration in higher moisture environments and cold-rain processes. The observational and modeling studies will be helpful for in depth understanding the role of aerosols and their interactions with clouds on the hydrological cycle by modifying the cloud properties and monsoon intraseasonal oscillations. The process studies must be beneficial for the realistic parameterization of cloud processes in the NWP model and can provide a pathway for increasing the grid point ISM rainfall skill through fundamental basic research on cloud microphysical processes.