WRF-Chem lightning NOx parameterization at Florida State University: FSULNOX

Nitrogen oxides (NOx) produced by lightning (LNOx) play an important role in atmospheric chemistry, including the formation of tropospheric ozone (O3). Chemical models such as the Weather Research and Forecasting (WRF-Chem) model can simulate some aspects of ozone's chemistry, but to produce accurate O3 concentrations, it is important to accurately specify LNOx. Although lightning is a major source of NOx, WRF-Chem does not include lightning or the production of the resulting NOx. The goal of this study is to improve the forecast of tropospheric ozone in WRF-Chem by adding a module that parameterizes lightning occurrence and the resulting formation of NOx by lightning. The parameterization is designed for use on the regional scale.

Previous studies have shown that radar-derived storm height and other parameters are strongly correlated with lightning flash rate. Using data from the Kennedy Space Center Lightning Detection And Ranging (LDAR) Network and WSR-88D radar, a lightning parameterization has been developed for use in WRF-Chem. The parameterization uses a relation between lightning flash rate and storm top height above the freezing level to predict lightning flash rates. The predicted flash rates and a NOx production term then determine the two dimensional LNOx pattern. Finally, we have constructed climatological vertical distributions of lightning sources measured by the LDAR network at Kennedy Space Center as a function of storm top height above the freezing level. These vertical profiles are used to distribute the LNOx in three-dimensions at each model grid point. Values of NOx and ozone calculated by WRF-Chem, with and without the addition of the lightning parameterization, will be presented. Results will be compared to aircraft data from the INTEX-A project.