Convective Cloud Lifecycle and Merging Behavior in Sea-Breeze Environments: Insights from TRACER observations and WRF Simulations

We characterize convective clouds associated with sea-breeze circulations (SBC) using multi-agency observations and multi-case ensemble model simulations. The focus is on assessing convective cloud lifecycle properties and their merging behavior, as well as the environmental conditions they are embedded in, particularly SBC features. In total, 46 SBC days over the Houston-Galveston region are selected and simulated using the Weather Research and Forecasting (WRF) model at 1 km horizontal grid spacing. Advanced techniques, including change-point detection, a Lagrangian cell tracking method, and a newly-developed cell merging and splitting detection algorithm, are applied or developed for this study.

Our findings indicate that the WRF model well represents the thermodynamic conditions, as well as SBC timing and intensity. However, for the associated convective cells, WRF overestimates the 30-dBZ echo top height (ETH), cell area, and maximum radar reflectivity compared to radar observations. This overestimation is primarily due to under-resolved entrainment processes and an overestimated cell merging frequency. Furthermore, the model exhibits a deficiency in simulating congestus clouds, showing a more rapid transition from shallow to deep convection compared to observed behavior. Moreover, sounding observations indicate a moister environment preceding convective clouds with merging events, which are linked to stronger, deeper, and wider clouds. Conversely, in simulations, the merging process does not produce higher or longer-lived cells, as many cases already exhibit high ETH (>10 km) before merging, where updrafts can no longer increase.