Characterization and Microphysical Impacts of Cloud Top Generating Cells During WINTRE-MIX

Cloud Top Generating Cells (CTGCs) are small-scale convective structures typically found near or at the tops of clouds. These cells play a crucial role in precipitation processes at subkilometer scales, which are often not captured by standard operational networks or numerical weather prediction models. Previous studies suggest that high-resolution radar data is needed to detect the presence of CTGCs due to their small size and complex dynamics.

In this study, we aim to provide insights into their dynamic processes of CTGCs to better understand their role in cloud microphysics and precipitation formation. We use ground-based polarimetric Doppler radar observations from three radars (one C-band and two X-band) to characterize the spatial and temporal evolution of CTGCs. Observations were conducted within a 5 to 7 km deep mixed-phase cloud on 22 February 2022 as part of the Winter Precipitation Type Research Multiscale Experiment (WINTRE-MIX). We analyzed the evolution of CTGCs, focusing on their size, spacing, and the signatures they produce in radial velocity and dual-polarization variables, including radar reflectivity (Z), differential reflectivity (ZDR), and correlation coefficient (RHOHV). Environmental soundings and a vertically pointing microwave radar (MMR) were also employed to provide comprehensive vertical profiles of these cells.

Our findings indicate that CTGCs predominantly occur at cloud top temperatures between -15°C and -30°C and are uniformly distributed over an approximately 50 x 50 km area, with horizontal widths ranging from 0.7 to 3.1 km. Reflectivity values within CTGCs typically range from 0 to 15 dBZ, showing an increase and decrease of approximately 6 dBZ from the edges to the center of the generating cell. Further analysis reveals a negative correlation between Z and ZDR and a positive correlation with RHOHV, suggesting that riming and aggregation are prevalent processes within CTGCs. Ongoing research will focus on further understanding the interaction between CTGCs and the melting layer, as well as their impact on surface precipitation.

By integrating multiple radar observations and environmental soundings, this study aims to enhance our understanding of CTGCs’ microphysical properties and their potential impact on precipitation formation. These insights are expected to contribute to refining weather forecasting models and improving our comprehension of cloud processes under similar atmospheric conditions, underscoring the importance of considering subkilometer CTGCs in numerical model parameterizations.