UC Berkeley

The microphysical processes involving water droplets and ice crystals in clouds are too small to be explicitly simulated by climate and weather models. Nevertheless, they play a critical role in the large-scale energy balance of the Earth and its atmosphere, as well as smaller-scale phenomena such as storms. This dissertation examines the impact of microphysics on the latter, specifically extreme precipitation and lightning. Climate change threatens to exacerbate such events, making the understanding of such extremes crucial.

We focus primarily on the effects of microphysical processes as they are simulated in a superparameterized climate model, which is better suited to studying clouds and the associated extreme weather events than conventional models. We find statistically significant differences in extreme precipitation rates via two separate mechanisms when replacing one commonly used microphysics parameterization with another. We also find that the sign of changes in lightning flash rates with global warming depends on the microphysics representation used. Finally, we employ observations to address a longstanding question about the necessity of ice as a precursor of lightning. With the data available it is concluded that there is insufficient evidence to suggest that thunderstorm electrification can occur in the absence of ice.