Application of a New Lightning-NOx Parameterization in a Hector Thunderstorm Cloud/Chemistry Simulation

The 3-D WRF-AqChem model was used to simulate the Hector thunderstorm observed on 16 November 2005 during the SCOUT-O3/ACTIVE campaign. A lightning-produced NOx parameterization, which was previously developed for cloud-resolving models and tested on several midlatitude and subtropical convective events (DeCaria et al., 2005; Ott et al., 2007, 2010), was applied to the Hector thunderstorm. Undisturbed air observations were provided by research aircraft and aided in constructing composite initial chemical profiles. Convective transport processes were evaluated using tracer species, such as CO and O3. Initially, the LINET provided observed lightning flashes as model input and a lightning placement scheme was used to inject the resulting NO into the simulated cloud volume. Various scenarios of NO production per cloud-to-ground and intracloud flashes were tested. The best estimate of NO production per flash was determined by comparing the resulting NOx mixing ratios from each scenario with upper tropospheric anvil observations. Subsequently, a new parameterization of lightning-produced NOx (Barthe and Barth, 2008) was tested in the Hector simulation. Unlike the previous parameterization, lightning-producing cells are identified with a vertical velocity threshold, the precipitation and non-precipitation ice mass flux product provides an estimate of the flash rate per cell, and the NO source location is filamentary versus volumetric. The predicted flash rates and the resulting NOx produced in the Hector simulation were compared against observations in an effort to provide a better understanding of lightning-generated NOx production in the tropics. The Hector simulation represents the first test of this new parameterization in a tropical environment.