The Mechanism of Precipitation Formation in Northeastern Colorado Cumulus III. Coordinated Microphysical and Radar Observations and Summary

Abstract

Much of the previous work which has led to the conclusion that coalescence is the dominant precipitation forming mechanism in cumulus clouds is reviewed. Observations in northeastern Colorado from several independent methods of investigation are summarized to show that in northeastern Colorado the ice (Bergeron–Findelsen) process is in all probability the dominant mechanism in spring and summer cumuli in their early and intermediate stages of development. Results of microphysical observations coordinated with simultaneous radar observations are presented. The microphysical observations in clouds with observed effective reflectivities of up to 40 dBZ show that the observed reflectivities can be accounted for by measured ice particle sizes and concentrations. Liquid precipitation elements are not necessary and have been observed only rarely in these clouds except below the melting level. Possible explanations of the differences between clouds in northeastern Colorado and those in other areas are discussed. The rarity of liquid precipitation particles coupled with the general inefficiency of the ice process at temperatures warmer than −10C suggests that there is potential for rainfall enhancement in the clouds in northeastern Colorado.