Pre-monsoon aerosol intensification and enhanced atmospheric warming over the South-Eastern Arabian Sea

The South Eastern Arabian Sea (SEAS) along the west coast of India often shows intense aerosol build-up during the pre-monsoon season, marked by brief Aerosol Optical Depth (AOD) surges. As such events are found crucial to regional weather, this study examines the causes and effects of these events, integrating data from MODIS, CALIPSO, and INSAT-3D satellites, MERRA-2 reanalysis, and back-trajectory analysis for the period 2015-2017. High AOD events over the SEAS are linked to elevated aerosol layers between 1 and 4 km, mainly polluted dust and smoke, with pure dust in most of the cases. These events are found to be fuelled by pronounced shifts in wind circulation, increased convergence, strong updrafts, and higher humidity above ~ 1.5 km, aiding aerosol transport from upwind biomass-burning and industrial regions. Absorbing aerosols like black carbon (BC) and organic carbon (OC) strongly correlate with sulphates (SU), suggesting common origin and mixed aerosol type, pointing towards higher absorption effects. This together with the amplifying influence of underlying clouds increases the positive Atmospheric Radiative Forcing (ARF_ATM) from 4 to 6 W m⁻² on normal days to 8-12 W m⁻² during high-pollution events. This increased radiative forcing heats the lower atmosphere (0.3-2.5 km) by about 1-2 K, as seen in temperature profiles, and its changes closely follow the observed temperature variations. These exciting observational results highlight the strong role of absorbing aerosols in high pollution events modifying the atmospheric thermal structure, with probable implications on aerosol-cloud-precipitation interactions and weather patterns along the west coast of India.