Ice particle concentrations in clouds.

Abstract

Measurements and observations have been made on the development of ice in 90 cumuliform (cumulus and cumulonimbus) and 72 stratiform (altocumulus, altostratus, nimbostratus, stratocumulus, and stratus) clouds. Ice particle concentrations significantly in excess of those to be expected from ice nucleus measurements (i.e., ice enhancement) were measured in 42 of the cumuliform and 36 of the stratiform clouds. For the complete data set, and for cloud top temperatures (TT) between -6o and -32oC, the maximum concentrations of ice particles (Imax in L-1) in the clouds were essentially independent of TT (r = 0.32). However Imax was strongly dependent on the broadness of the cloud droplet size distribution near cloud top. In light of the findings, it is postulated that ice enhancement is initiated during the mixing of cloudy and ambient air near the tops of clouds and that it is associated with the partial evaporation and freezing of a small fraction of the droplets approximately more than 20mu m in diameter. -from Authors