Observational and simulated cloud microphysical features of rain formation in the mixed phase clouds observed during CAIPEEX

Cloud microphysical observations of rain formation in mixed phase monsoon clouds (from 10 to −9°C) using instrumented aircraft during Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) are presented. The drop size and particle size distributions are broader in the mixed phase region, indicating efficient growth of liquid as well as ice phase. Aircraft observations noticed higher ice particle concentrations in Hallet–Mossop zone (−3 to −8°C) with existence of smaller and larger cloud droplets, rimed needles columns, and graupel particles. Observations strongly suggested the active presence of Hallet–Mossop (1974) process in this cloud. The higher correlations found between slope and intercept parameters of exponential size distributions can be attributed to the efficient secondary ice production as well as to the aggregation growth of ice particles. Large Eddy Simulation (LES) of these clouds are compared with observed cloud microphysical properties, also illustrated the important role of Hallet–Mossop (HM) process and its link with warm rain and graupel formation. The raindrop freezing plays a crucial role in graupel formation in early stage of ice development. The observed mean values of microphysical parameters including liquid water content, ice water content, ice number concentrations, and reflectivity showed good agreement with model simulations. Primary ice nuclei have only a minor role in the total ice mass in these clouds. •Aircraft observations in mixed phase clouds are presented, the Hallet–Mossop process was highly active in this clouds.•The ice particle size distribution properties are presented showing aggregational growth was dominating.•The LES simulations are presented and compared with observations; it shows two-stage ice formation in monsoon cloud.•The freezing of supercooled raindrops plays an important role in graupel formation and hence in Hallet–Mossop process.