Unveiling the Interaction between Aerosols and Deep Convection through Joint Cell-Thermal Tracking Analysis of Large Eddy Simulations from the TRACER Field Campaign (Invited Presentation)

The TRacking Aerosol Convection Interactions ExpeRiment (TRACER) represents a comprehensive field measurement campaign conducted over the Houston metropolitan area from June 1 to September 30, 2022. This study leveraged the NASA-Unified Weather Research and Forecasting (NU-WRF) model with enhanced capabilities of Electrification, Polarimetric radar Instrumental simulator, and Cloud condensation nuclei (NU-WRF EPIC), to perform regional Large Eddy Simulations (LES). During this period, a few sea-breeze-driven isolated deep convective events were identified as "golden cases" due to the availability of high-quality cell-tracked radar and lightning observations. We conducted sensitivity experiments on these golden cases, utilizing NU-WRF EPIC simulations under varying aerosol conditions—both clean and polluted—as determined by ground-based aerosol observations. By employing the Tracking and Object-Based Analysis of Clouds (TOBAC), we rigorously traced the development of cumulus thermals, aligning them with the cell tracking algorithm.

Our findings reveal that polluted aerosol conditions induce faster updraft velocities, enhance cloud droplet concentrations, reduce raindrop formation, and increase the presence of ice crystals and graupels within the thermals. These thermals exhibited distinct vertical transitions and temporal evolution patterns, suggesting that thermal chains play a critical role in shaping convective microphysics under varying aerosol backgrounds. Furthermore, the polluted conditions not only raised the initiation levels of thermals, altering the cloud thermodynamic environment, but also decreased the frequency of isolated convective cells. These insights underscore the need for a deeper understanding and parameterization development of cumulus thermals to accurately represent the feedback mechanisms between convective processes, thermodynamics, and aerosols within the climate system.