Microphysics of deep tropical convective clouds observed over India Part 2 : simulations with a high resolution spectral bin microphysics model (The HAMP contribution)

During summer 2009 a large set of unique in-situ measurements of deep convective clouds over India has been performed within the framework of the CAIPEEX (Cloud Aerosol Interaction and Precipitation Enhancement Experiment) project of the Indian Institute of Tropical Meteorology in Pune, India. The measurements were carried out up to heights of 8 km over the surface. The clouds developed in extremely humid atmosphere. The CCN concentrations were measured as well. In many cases concentration of aerosols was as high as in pyro clouds in the area of biomass burning. In these cases the droplet size distributions were extremely narrow. In spite of extremely high humidity and low cloud base level, high CCN concentrations lead to the fact that first raindrops form at ~ 5 km level and the first graupel form at heights of 7 km. In the simulations of these clouds performed using a Hebrew University Cloud model (HUCM) the droplet size distributions and their evolution with height were successfully reproduced. The role of aerosols, including giant CCN as well as ice cloud structure on precipitation is investigated. The vertical profiles of effective radius are calculated and compared with the observed values. The results of in-situ measurements provide evidence for the validity of the HAMP hypothesis that an increase in the aerosol concentration at the TC periphery increases the amount of supercooled water at upper levels and intensifies convection. The numerical simulations presented indicate that the model with spectral bin microphysics is able to reproduce these unique in-situ measurements, so that the TC model based on this microphysics can serve as a benchmark one for investigation of aerosol effects on TC structure and intensity as well as for calibration of different bulk-parameterization schemes.