Precipitation processes over Indian region under different environmental conditions from in situ measurements

Abstract Large-scale transport of air mass modulates the weather by altering the cloud and precipitation microphysics of convective clouds. This study examines how oceanic and continental air mass advected into the convective cloud system determines hydrometeors' vertical distribution using in situ airborne observations from the Cloud-Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) during 2010. Maritime air mass from the Bay of Bengal favours a clean atmosphere (CA) that supports clouds with fewer droplets, and the effective radius crosses above 12 μm below the 10 °C temperature level. Thus CA is mainly characterised by moderate precipitation efficiency and broader hydrometeors size distribution spectra. The mixing of air mass from the Arabian sea, Bay of Bengal, and central Indian region results in a moderately polluted atmosphere (MPA), enhancing convective cloud depth and favours mixed-phase processes and equally strong updrafts and downdrafts. As the concentration of sea salt, dust particles, moisture content, and convective available potential energy (CAPE) increases, MPA profoundly supports the primary and secondary ice nucleation inside the convective system. Despite CA and MPA, wide hydrometeor size distribution is absent in a highly polluted atmosphere (HPA), primarily evolved from continental air mass. We noticed an absence of larger raindrops inside clouds developed in HPA, indicating reduced collisions, making them less efficient with the precipitation process. The raindrop size distribution under the three environmental conditions showed distinct characteristics, implying contrasting cloud microphysical processes and precipitation efficiency.