Temporal Evolution of Cloud-Top Generating Cells: A Case Study

Cloud-top generating cells (CTGCs) significantly influence winter precipitation, yet their complete life cycle remains poorly characterized observationally. This study analyzes the temporal evolution of CTGCs during a winter storm using X-band dual-polarization radar data from the Winter Precipitation Type Research Multiscale Experiment (WINTRE-MIX) field campaign. By tracking reflectivity (Z_e) perturbations between 5.5 and 8 km MSL, we identified a distinct three-stage population life cycle spanning;1.7 h. The observed CTGCs formed in two distinct spatiotemporal groups, indicating organization influenced by mesoscale environmental variations. Dual-polarization radar signatures indicated a microphysical progression from initially heterogeneous particles undergoing aggregation and riming, to sorting in mature cells, and finally to preferential sedimentation during dissipation. During the initiation stage (12–30 min), numerous small (;0.5 km² ) CTGCs formed. As they transitioned to the mature stage (54 min), adjacent CTGCs merged to form larger contiguous features or clusters (up to 60 km² ) with well-defined microphysical sorting}aggregates concentrated in the core and pristine crystals concentrated in the surrounding shroud. The subsequent dissipation stage (36 min) featured preferential sedimentation of aggregates from the CTGCs, leading to decreasing cell size and number. Environmental factors potentially played key roles throughout this evolution: Vertical wind shear likely contributed to cell merging and elongation, while moisture depletion appeared to limit further development and initiate dissipation. In this case study, we provide a quantitative, observationally based description of the complete life cycle of the observed CTGC population, highlighting the role of merging processes and evolving microphysical characteristics throughout their lifespan.