Unraveling Cloud-Top Generating Cells Properties using 20 m LES

Cloud-top generating cells, characterized as small regions of enhanced radar reflectivity near the cloud top with trails of precipitating hydrometeor below, are frequently observed structures in various types of cloud systems, from wintertime orographic clouds to Southern Ocean clouds and winter cyclones. These structures are hypothesized to provide favorable conditions for the formation and growth of natural ice, which is critical for winter precipitation. Despite their significance, identifying and understanding cloud-top generating cells remains a challenging task. This is largely attributed to an incomplete understanding of their formation mechanisms and the associated microphysical and dynamical properties.

In this study, we conducted a 20-m Large Eddy Simulation (LES) of winter orographic clouds in Idaho during SNOWIE (Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment) using WRF. The Cloud Resolving Model Radar Simulator (CR-SIM) was used to convert model geophysical quantities from LES into radar signals. This approach offers a commensurate, apples-to-apples comparison between model simulations and cloud radar observations along the University of Wyoming King Air’s flight track. We applied and compared various generating cell identification algorithms, jointly analyzing radar observables from the radar simulator, such as radar reflectivity and spectrum width, with the associated microphysical and dynamical fields obtained from LES. This comprehensive analysis generates a unique dataset that helps unravel the key processes and intrinsic physical properties characterizing generating cells.