Linking cloud dynamics and microphysics on subgrid scales

Description

Intrinsic interactions between dynamical and microphysical processes in clouds result in correlations between vertical velocity and microphysics variables on scales that are unresolved in coarse-resolution models. Parameterizations representing effects of subgrid variability on tendencies of grid mean variables often make implicit or explicit assumptions on the strength of these correlations. A recently developed parameterization for subgrid hydrometeor transport, for example, prescribes different correlations in convective updrafts/downdrafts and stratiform regions [Wong et al., 2015; Wong and Ovchinnikov, 2017]. In this presentation, we explore the relationships between vertical velocity and mass and number mixing ratios of various hydrometeors in cloud-resolving model simulations of continental and maritime convection in a domain comparable to a GCM column. Strong updrafts and downdrafts are found to be associated with larger-than-mean condensate amounts, while quiescent regions most often contain smaller-than-mean amounts. Within updrafts and downdrafts, vertical velocity also has a consistently stronger correlation with precipitating hydrometeor mixing ratios than in stratiform regions. These features of dynamics-microphysics correlations persist over the lifetime of the simulated convective events and, therefore, can be justifiably included in parameterizations. References: Wong M., M. Ovchinnikov, and M. Wang. 2015. "Evaluation of subgrid-scale hydrometeor transport schemes using a high-resolution cloud-resolving model." Journal of Atmospheric Science 72: 3715–3731, doi: 0.1175/JAS-D-15-0060.1. Wong, M. and M. Ovchinnikov. 2017. "A PDF-based parameterization of subgrid-scale hydrometeor transport in deep convection." Journal of Atmospheric Science (in press).