Measurement of Flare Size Distribution and Simulation of Seeding Effect with a Spectral Bin Parcel Model

Cloud seeding experiments were conducted during the Cloud Interaction and Precipitation Enhancement Experiment (CAIPEEX) near Hyderabad, India, in 2011. Here, we report both the background aerosol and hygroscopic flare size distributions measured during the airborne experiment. The size distributions were measured in the diameter (D) range of 0.02–50 µm; both ultra-fine (0.02 µm < D < 0.1 µm) and coarse mode (D > 0.5 µm) particles were in greater concentrations in flare than in the background aerosols. The sensitivity of cloud droplet growth to the flare particle size distribution is studied with the help of a 2000-spectral bin parcel model, where droplet growth, collisions, and formation of raindrops are represented. The simulation results indicate the rapid formation of warm rain in cloud due to the tail effect of activation of coarse mode aerosols into large size cloud droplets. At higher altitudes, in-cloud activation and a secondary mode in drop size distribution are noted. For a given cloud base updraft, the rain flux increases with the increase in the coarse mode aerosol concentrations. However, for a given coarse mode aerosol concentration, the rain flux decreases with increasing cloud base updrafts.