Mechanical and Civil Engineering Seminar: PhD Thesis Defense

Abstract:

Feedbacks between a warming atmosphere, emission of aerosols, and clouds and precipitation are some of the most difficult aspects for climate models to accurately capture. While climate models operate at resolutions of tens or hundreds of kilometers, many of the physics that determine how and where clouds form or precipitate function at the micron droplet scale. Due to this disparity in physical scales, most of these cloud physics must be modeled with only a few approximate quantities and physical equations. These simplifications lead to large uncertainties about climate forcings such as the sensitivity of global warming to human-emitted aerosols.

This work presents several promising new techniques for modeling and understanding hydrometeors in the climate system, with a particular focus on processes that involve collisions between droplets. First, I extend a high-complexity high-fidelity Lagrangian microphysics method to represent the process of breakup, in which colliding droplets fragment upon collision. Next, I introduce two new methods which attempt to reduce the assumptions inherent to modeling droplet coalescence, in which colliding droplets combine to form a larger drop. The first method uses a spectral finite element approach, while the second generalizes this technique using a method of moments to create a fully flexible microphysics scheme. Finally, I turn to remote observations of clouds, aerosols, and lightning over busy shipping regions to offer new techniques for quantifying aerosol-cloud interactions from creative data resources. This combination of high-fidelity modeling tools, observational data, and efficient numerical methods offers a path toward improving our understanding of the role of cloud microphysics in our climate system.