Simulating Troposphere-Stratosphere Exchange and Chemical Transport during Supercell and Mesoscale Convective Events

Deep convective clouds exert a substantial influence on the upper troposphere and lower stratosphere (UTLS) through their rapid transport of aerosols and chemical compounds from the planetary boundary layer (PBL) to the UTLS region. The consequences for air quality and atmospheric chemistry are contingent on the magnitude of this transport. We have analyzed two observed cases of deep convection during the Deep Convective Clouds and Chemistry (DC3) campaign: a supercell in Oklahoma on May 29, 2012, and a mesoscale convective system (MCS) on June 11, 2012. Our primary objective is to assess the rate of simulated trace gas transport from the PBL to the UTLS; and secondly, to evaluate the efficacy of a novel lightning data assimilation (LDA) technique. To accomplish these objectives, we employ the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), configured with 70 vertical levels and resolutions of 36 and 12 km to replicate the deep convection scenarios. To improve simulation accuracy, the LDA technique introduced by Heath et al. (2016) is employed alongside a WRF-Chem simulation without LDA. The utility of the LDA scheme is evaluated through comparisons of simulated precipitation with STAGE-IV and IMERG Final Run precipitation observations. In addition, GOES-13 brightness temperatures are compared with simulated cloud top heights. Our findings reveal that the LDA technique significantly refines the timing, development, and positioning of deep convective clouds. Moreover, it increases the correlation between airborne observations and simulated CO transported from the PBL to the UTLS via deep convection, exhibiting pronounced improvements in both supercell and MCS cases in the upper atmosphere. Notably, the supercell event exhibits greater CO flux densities by 13.37% and water vapor flux densities by 42.94% within the near-surface layer compared to the MCS event, indicative of greater vertical transport per unit area. In contrast, the MCS event has greater CO transport to the UTLS as the storms evolve, yet displays weakened mass flux density within the storm area, attributed to the influence of a rear inflow jet descending from the mid-troposphere. Additionally, the MCS event reveals a weaker troposphere-to-stratosphere transition in terms of mass flux compared to the supercell event. Our study underscores the pivotal role of lightning data assimilation in enhancing simulations of troposphere-stratosphere exchange and chemical transport during supercell and mesoscale convective events. The WRF-Chem simulations offer valuable insights into the intricate dynamics of these atmospheric phenomena.