Coarse-scale Convective Transport of CO and O3 Over 36 Hours Above Southern United States

Ozone distribution in the UTLS region is an important factor in the heat budget for the LT. Above areas with heavy industrial activities and other anthropogenic sources, the UT can potentially experience anomalously high pollutant composition when deep convection extracts boundary layer air and detrains it at high altitude. Though healthy for boundary layer air quality, such migration of pollutants complicates the ozone budget in UTLS. Therefore reliable budgets require dependable models for chemical transport in the region of convection and reactions. Detailed dynamic scheme that resolve convection show great promise for accurately simulating and understanding the transport of relevant chemical constituents, while parameterized convective schemes are still required for coarse resolution simulations. While there is an abundant choices of heavily tested microphysics and grid-scale dynamic schemes, some convective parameterization methods call for more validations. This is a much more prominent issue in lower resolution runs, where sub-gridscale convection transports of trace gases must be parameterized and seldom assessed. In this way, measurements of the chemical species under such settings can provide a critical test of the fidelity of convective transport schemes. Coarse-resolution (Δ x=36km) simulations using Weather Research and Forecasting model coupled with Chemistry (WRF-chem) are done to quantify how well different convective parameterization schemes performed. Results are compared to observation of CO and O3 profile from Tropospheric Emission Spectrometer (TES). We focus on the case of the 36 hour period in the southeastern United States on Aug 23-24, 2006, which coincides with heavy convective activity over Oklahoma and Arkansas. Using the Grell-Deveyi parameterization scheme in a low resolution simulation, result shows large amount of water vapor transported into the UTLS region, where it is retained further at this level by the summer anticyclone of Southern United States centered above Houston, TX. Yet, no comparable amount is observed in another simulation done without any convective parameterization. The TES CO data suggest these convective anomalies indeed occur, and as such the transport of chemical CO and O3 that accompanies the water vapor detrainment provides a strong local enhancement of the ambient concentrations because of the rapid ventilation of pollutants emitted from the surface. This work highlights the need to understand the convective transport in regional trace gas budgets, and that some care is needed to ensure the convective transport is adequately accounted for in models where horizontal resolutions are limited above the typically scale of a convective system.