On the source of elevated pollution layer: A case study using CAIPEEX observations and WRF-chem

Atmospheric aerosols alter the radiation balance by absorption/scattering of solar radiation, and indirectly by modifying the cloud microphysical properties. Observations during Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) provide a unique opportunity to investigate the aerosol- cloud interaction in a dry to wet transition phase. It is observed that, the aerosol loading increased over the central Indian region in spite of the increase in surface rainfall. The effect of aerosol entrainment into the study area is investigated by separating the mean flow and area average aerosol concentration. Elevated aerosol layer and its effect on cloud optical depth over selected regions are discussed. Sensitivity experiments with the dust source emission in the WRF Chem simulations indicate that resulting elevated pollution layers have impacted the supercooled liquid and especially the ice cloud distributions. The peninsular Indian region had less cloud cover in response to an increase in dust emissions, while over Bay of Bengal and over the Arabian Sea there was marginal increase in the cloud cover. These differences are mainly attributed to induce changes in the dynamics as a result of different heating rates.