Suppression of warm rain by aerosols in rain-shadow areas of India

Abstract. Aircraft observations of clouds and aerosols were conducted during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) executed by the Indian Institute of Tropical Meteorology over the Indian subcontinent during the period of May–September 2009. Existence of aerosol layer with large concentrations of cloud drop condensation nuclei extended up to heights of 4 to 5 km was observed over the rain shadow areas to the east of the Western Ghats over central India. The thick aerosol layers were observed to suppress the formation of warm rain in convective clouds up to heights of about 7 km, where mixed phase precipitation formed. This prevented clouds that did not exceed this height from precipitating significantly. This might invigorate the very deep clouds on expense of the smaller clouds. The aerosol radiative effects are suspected to decrease the surface heating and hence the available energy for propelling the convection. The net effect of the aerosols on the rainfall amounts is unknown due to the complexity of the effect, but it is suspected to be detrimental in an area where the rainfall is critical to the livelihood of the inhabitants. This requires continuation of this research.