Evaluation of the importance of wet scavenging for the May 29, 2012 DC3 severe storm case using results from WRF-chem simulations

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Wednesday, 5 February 2014: 11:15 AM
Room C113 (The Georgia World Congress Center )
Megan Marie Bela, University of Colorado, Boulder, CO; and M. C. Barth, O. B. Toon, A. Fried, H. Morrison, K. Pickering, K. A. Cummings, Y. Li, D. Allen, and K. W. Manning

Deep convective thunderstorms affect the vertical distribution of chemical species through vertical transport, lightning-production of NOx, wet scavenging of soluble species as well as aqueous and ice chemistry. This work focuses on the May 29 Oklahoma thunderstorm from the DC3 (Deep Convective Clouds and Chemistry) field campaign. WRF-Chem simulations at cloud parameterizing scales (dx=15km) and cloud resolving scales (dx=3 and 1km) are conducted to investigate wet scavenging of soluble trace gases. Two different wet scavenging schemes are coupled to the Morrison microphysics scheme and MOZART chemistry. The first, based on Neu and Prather (ACP, 2012), tracks dissolved species in cloud droplets and precipitation and releases species to the gas phase from evaporating precipitation. However, it does not distinguish between precipitating liquid and ice, and species are completely retained upon hydrometeor freezing. The second, described in Barth et al. (JGR, 2001), tracks solute in individual liquid and frozen hydrometeors, and a new capability to specify the fraction of each species that is retained in ice upon hydrometeor freezing is added. The simulated meteorology, evaluated with the NEXRAD radar reflectivity, is shown to represent the structure and evolution of the storm, although the simulated storm triggers about an hour early, has a larger area of high reflectivity and extends further north than observed in NEXRAD. Vertical distributions of trace gases with varying solubilities within the storm and immediately surrounding the storm are compared with observations from the GV and DC-8 aircraft in storm inflow and outflow regions. Using the Neu and Prather scheme or using the Barth scheme with zero or complete ice retention, observed mean vertical profiles of some soluble species in outflow are better represented in the model with scavenging, while others are overly scavenged. Finally, sensitivity studies are conducted to determine ice retention factors for each species and included in the Barth scavenging scheme to improve the model representation of convective cloud transport and processing of chemical species.