Role of monsoon intraseasonal oscillations in modulating extreme rainfall and aerosols over central India

This observational study diagnoses the influence of the monsoon intraseasonal oscillation (MISO) on aerosols and extreme rainfall events (EREs) in Central India, using the satellite datasets from CERES and GPM-IMERG, from 2003 to 2019. The research examines explicitly how MISO phases modulate aerosol optical depth (AOD) and the occurrence of EREs during the summer monsoon. We found that high AOD phases correspond to reduced ERE frequency, while low AOD phases see increased ERE occurrences, showing negative correlation. Also, a time lag of two phases in the variation between the rainfall amount from all the precipitation and the rainfall amount brought by EREs. The analysis extends to the effects of AOD on atmospheric dynamics and cloud properties across MISO’s eight phases. Increased AOD during active MISO phases is linked to altered atmospheric dynamics, notably affecting moisture convergence patterns associated with cyclonic and anticyclonic activities. Initially, the onset of the monsoon, marked by high aerosol loading and dry air, leads to reduced moisture convergence and fewer EREs. As aerosol levels increase, there is a notable rise in cloud fraction but with smaller cloud-water droplet sizes, which paradoxically minimizes the likelihood of EREs despite greater cloud coverage. The study highlights that high aerosol concentrations combined with substantial cloud cover can lead to surface and lower atmospheric cooling, potentially altering monsoon circulation and convection patterns in subsequent phases marked by stronger winds and higher aerosol densities.