Assessing Subgrid Convective Transport and Mass Flux in Deep Convective Clouds Using Parameterized WRF-Chem Simulations

Deep convective clouds significantly impact the upper troposphere and lower stratosphere by rapidly transporting aerosols and chemicals from the boundary layer. The impact on upper troposphere/lower stratosphere composition depends on the magnitude of this transport. Climate and regional air quality models typically use a coarse resolution that requires the use of convective parameterization schemes (CPS), which may not adequately capture this rapid transport. We will present the results of WRF-Chem simulations of carbon monoxide (CO) (grid spacings of 36 and 12 km) run with convective parameterizations for two cases of deep convection during the Deep Convective Clouds and Chemistry (DC3) campaign: a supercell on 29 May 2012 and a mesoscale convective system (MCS) on 11 June 2012. To enhance the accuracy of the simulated deep convection, we employ a novel lightning data assimilation (LDA) scheme. This scheme uses lightning data to activate or suppress the Kain-Fritsch (KF) cumulus scheme, serving as a proxy for thunderstorm electrification that is not explicitly simulated by the model. The CPS controlling LDA technique (Heath et al. 2016) is used to couple subgrid-scale convective transport to the KF cumulus scheme in WRF-Chem and thereby provide consistency with subgrid convection. The subgrid-scale and grid-scale contributions to the vertical transport of CO will be presented. The time tendency of CO is also calculated, with results indicating that the subgrid-scale contribution in the convective area becomes as great as 90% during the mature stage of the supercell storm, and 55% during the mature stage of the MCS. A dipole structure of vertical transport is detected in the non-supercell convective area. Moreover, the entrainment rate is an important parameter in convective parameterizations, affecting the vertical transport of heat and moisture in convective clouds, and thereby the structure of the cloud. Thus, we will also present an assessment of the relationship between the entrainment rate and the time tendency of CO. Lastly, subgrid-scale mass fluxes are critical to the vertical redistribution of pollution due to unresolved deep convection. Therefore, we will present differences in convective mass flux during deep convection and their varying properties in the supercell and MCS cases.