Cloud particle measurements in thunderstorm anvils and possible weather threat to aviation

The characteristics of cloud particles in thunderstorm anvils have not been extensively studied. Most previous meteorological studies of thunderstorms have focused on regions of the storm that produce precipitation on the ground. The particles in the anvil typically fell slowly from high altitude and evaporate before reaching the ground. Results from analysis of aircraft observations in the anvils of mid-latitude and tropical thunderstorms are discussed. Aircraft and radar observations are combined with model results to show that most anvils associated with small, "garden-variety" thunderstorms contain low (< ~0.4 g m^-3) mass concentrations of ice particles. In larger, more intense mid-latitude storms, anvils may contain ice water contents from 1 →3 g m^-3. The mean-maximum particle dimension in the anvil region of the more intense storms showed a strong modal size of about 2 mm. The particles themselves appear to be ice crystals and aggregates of ice crystals (i.e., snow flakes). The ice particles and snow flakes are formed in the updrafts and carried aloft into the anvil. The mass concentration of ice particles decreases rapidly away from the center of thunderstorms. The measurements show that the ice water content decreases to less than half its peak value within about 10 km of the central region of the largest storms. The aircraft, radar and model results all suggest that the ice water content is well below 1 g m^-3 at a distance of ~50 km away from the central region of a thunderstorm (i.e., the region with high radar reflectivity).