Speaker: Kaitlyn Loftus (NASA/GISS)
Topic: Simplified representations of cloud rainmaking on Earth and other planets

Will a cloud transport any of its condensed mass to the surface as rain? If yes, what fraction? At what rate? Over what duration of time? These questions are basic outcomes of cloud evolution with consequences for both local weather events and planetary-scale climate; their answers, however, are complicated by the abundance of nonlinear, multi-scale processes connected to cloud rainmaking. Amidst this complexity, here I consider the liquid drop-scale (microphysical) perspective. I focus on simplified microphysical representations of cloud rainmaking necessary for improved conceptual understanding of cloud evolution and parameterizing microphysics in larger-scale models. Under generalized planetary conditions, I use the simplicity of how raindrops fall and evaporate to place constraints on rain initiation and efficiency independent of the complex processes governing raindrop growth. Under modern Earth conditions, I explore connections between global climate models’ longstanding and widespread too frequent drizzle bias and their shared conceptual assumptions in parameterizing liquid drop growth in clouds.