Collaborative Research: Dynamics of Unsaturated Downdrafts, Cold Pools, and Their Roles in Convective Initiation and Organization

Moist convections play a critical role in giving rise to clouds/rains and in determining the energy balance of the earth and the distribution of water resources. They also play a key role in forcing the circulation patterns, and thus are central to our understanding and prediction of weather and climate. Because these processes occur at spatial scales smaller than that of the grid sizes of global weather and climate models, they need to be related to large-scale flow statistically in numerical models, or represented by parameterizations. The success of parameterizations demands physically based and process-level understanding of the moist convective processes. This project focuses on one important aspect of moist convections, namely cold pools. When rain evaporates into unsaturated air, it cools the air and increases its density, causing it to sink to the surface and spread out horizontally as a density current. These density currents are known as cold pools. They can trigger new storms (which is responsible for the gusty winds and cooler air that one experiences preceding a storm), modify near-surface fluxes, atmospheric stability, and affect the characteristics and development of convective clouds. In this project, high-resolution numerical simulations that explicitly resolve the cold pools and processes that produce them are used along with innovative particle tracking to unravel the many factors that contribute to the birth, evolution, and demise of cold pools, as well as to quantify how cold pools modify the characteristics of moist convections and how to represent these effects statistically in global models of weather and climate.

Clouds and convection remain major sources of uncertainty in weather and climate predictions. By improving process-level understanding and representation of a key feature of convective clouds, this research will help reduce such uncertainties. This research will also strengthen collaboration between university scientists and train postdoctoral scientists, and contribute to the development of weather and climate models.