The Warm Rain Process in Convective Clouds Influenced by Regional Aerosol and Climate Change

Precipitation development in a convective cloud is a function both of the warm rain process in the lower part of the cloud, and the interaction of liquid and ice particles in the upper part of the cloud. Determining how these precipitation processes may change as the climate changes regionally requires detailed modeling. Global and regional climate models offer projections of how thermodynamic properties of the atmosphere might change in the future, but the influence of these projected thermodynamic differences upon precipitation processes in convective clouds has not been fully explored.

In this study, thermodynamic soundings from climate model runs performed over the past 30 years, and projected 30 years into the future, are used to drive a 1D cloud model that contains detailed warm rain calculations. The goal is to gain insight on how warm rain productivity may change in the lower part of convective clouds over the United States, and to target cases that would be the most interesting to study with larger-scale, more dynamically complex numerical models. The effects of regional variations of cloud condensation nuclei are tested in this 1D model by initializing it with published values measured in similar environments. The new modeling results are analyzed geographically by region, and the greatest increases in warm rain production are found in clouds forming over the eastern half of the United States. In addition, the results show that cases with a very productive warm rain process demonstrate little sensitivity to changes in cloud condensation nuclei, a result at odds with published studies where precipitation processes have been represented in less detail.

The present study was conducted as part of a new sophomore-level, research-oriented laboratory at Purdue University in the Atmospheric Science program.