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Lightning Module for use in WRFChem
A Research Project with the Weather Research and Forecasting Model

NOx produced by lightning (LNOx) is an important factor in the formation of tropospheric ozone. Chemical models such as WRFChem can simulate some aspects of ozone's (O3) chemistry, but to produce accurate O3 concentrations, it is important to accurately specify the LNOx. Although lightning is a major source of NOx, WRFChem does not include that aspect of lightning production. The goal of this study is to improve the forecast of tropospheric ozone in WRFChem by adding a module that parameterizes lightning occurrence and the formation of NOx by lightning.

Previous studies have shown that radar-derived storm height is strongly correlated with lightning flash rate. Using data from Lightning Mapping Arrays (LMAs) at several stations, together with data from WSR-88 Doppler radars, the relationship between lightning flash rate and convective storm height will be studied. LMAs provide information about both in-cloud and cloud-to-ground flashes. A lightning module for use in the WRFChem model will be designed based on this study. The module probably will contain an approximately second order power law fit between the flash rate and the radar reflectivity echo top above the freezing level. Once established, this relationship will be used to predict lightning flash rate in a particular area based on WRF-derived reflectivity. Finally, a module to calculate NOx production from lightning will be inserted into WRFChem and evaluated using data from previous NASA airborne field studies of atmospheric pollution. The relationship between lightning and NOx from previous studies will be used in this module.

Major Objective I

The primary objective is to gain a better understanding of the storm electrification process. Some of the questions to be answered include: