The Relationship between Vertical Velocity and Microphysical Process Rates in Deep Convection

Dynamical and microphysical processes are intimately related: rising motion cools the air and produces supersaturation, leading to cloud droplet formation and driving condensation of water vapor onto cloud and precipitation particles, while the release of latent heating associated with condensation and freezing in turn affects the dynamics through changes in buoyancy and hydrometeor loading. While one expects a relationship between the magnitude of vertical velocity and condensational processes, it is not obvious what this relationship is due to feedbacks at play amongst the dynamics and microphysics, and whether this relationship is robust across cloud types or environments. Enhancing our understanding of the relationship between vertical velocity and microphysical process rates, particularly for deep convection, would improve our characterization of and ability to observe convective mass fluxes and transports, microphysical processes, and cloud dynamics.

The goal of this research is to investigate the quantitative relationship between the magnitude of vertical velocity and microphysical process rates, with a focus on deep convective cloud types. In order to assess this goal, a suite of high-resolution, state-of-the-art cloud-resolving model simulations are examined. A variety of convective organizations and environments, ranging from ordinary tropical convection to severe midlatitude convective systems, are included in the analyzed simulation suite. Additionally, two different model platforms and multiple different microphysical schemes are utilized. The results show a surprisingly robust relationship between the magnitude of vertical velocity and the rate of condensation or deposition onto liquid and ice hydrometeors, and the relationship is consistent across convective types and among the different models and microphysical schemes. Furthermore, the relationship is found to be linear, and the slope of the linear fit is found to vary only with temperature. Relevant physical processes and implications of these results will be presented.