On the impact of thunder on cloud ice crystals and droplets

Abstract

Calculations are presented on the impact of thunder on cloud particles. The results show that the creation of a shock wave front near a lightning channel results in shattering of ice crystals, droplets, and dust aerosols, this being a yet unidentified mechanism for secondary ice production in clouds. At low altitudes shattering is more efficient. At the distance where the shock wave front decays to audio wave, another mechanism can cause agglomeration of particles. The cloud particles' characteristics appear to be not very suitable for extensive acoustic agglomeration if the sound pressure level (SPL) is below 120 dB. Nevertheless, even for SPL<120 dB, some agglomeration will occur. Agglomeration will occur readily if SPL > 135 dB at sound frequencies of 10 to 200 Hz. Agglomeration efficiency increases with height. More agglomeration will occur in pyroclouds, due to their large particle number densities. These results show that the electrical environment in clouds has, through thunder, effects on the size distribution and number density of ice particles and droplets, will hence influence thundercloud radiative properties, and may be a significant driver of secondary ice production. As global warming may influence the occurrence rate of lightning, a climate feedback may be induced by the mechanisms discussed here.