Melting and Evaporation of Hydrometeors in Precipitation from the Anvil Clouds of Deep Tropical Convection

Abstract

Five cases of horizontally uniform precipitation associated with anvil clouds were investigated using weather radar, rawinsonde, satellite and raindrop size data collected during the Global Atmospheric Research Program's Atlantic Tropical Experiment (GATE). The area of horizontally uniform precipitation was in each case characterized by rainfall rates of 1?10 mm h?1 in contrast to the 10?100 mm h?1 observed in convective cells. Concentrations of precipitation-sized ice particles above the melting layer and liquid water below the melting layer, together with observed particle spectra, suggest that aggregation occurs above the melting layer, and that riming occurs in sufficient amounts to produce graupel within the anvil cloud. All five cases exhibited distinct radar bright bands in the melting layer. Cooling rates associated with the melting in this 1 km thick layer near the base of the anvil cloud were 1-7 K h?1. These cooling rates were comparable to the 0.2?6 K h?1 cooling rates due to evaporation of raindrops below the melting layer, suggesting that melting as well as evaporation plays a role in the initiation and maintenance of a mesoscale downdraft beneath the anvil cloud.