Royal Netherlands Meteorological Institute
Section of Atmospheric Composition
In order to describe the production of nitrogen oxides (NOx) by lightning in chemistry-transport models the spatial and temporal distribution of this NOx source needs to be specified. Various meteorological model parameters can be used as a proxy for specifying this distribution. In order to determine the most suitable parameter as a proxy for lightning, we have correlated different meteorological quantities from the ECMWF model, such as convective precipitation and cloud top height, with ground-based lightning observations made during the EULINOX project. Convective precipitation gave the best correlation for summer conditions over Europe. Using the established relationship between convective precipitation and lightning intensity, we have tested different vertical distributions of the NOx lightning source in the global chemistry-transport model TM3. The model simulated NO fields have been compared with the NO observations made during the 1998 EULINOX and the 1997 POLINAT/SONEX campaigns. We found that a prescribed lightning NOx profile gave the best agreement with the observations. The observations covered various conditions: typical background situations, inside thunderstorms, and the outflow of thunderstorms of various ages. The model underestimated the NO concentrations in cases of fresh lightning NOx, likely due to its insufficient spatial and temporal resolution, but under most other circumstances the new parameterisation performed reasonably well, and is a clear improvement over the previously used parameterisation based on cloud top heights.
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