Improvement and evaluation of the parameterisation of nitrogen oxide production by lightning

In order to describe the production of nitrogen oxides (NOx) by lightning i n 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 determ ine the most suitable parameter as a proxy for lightning, we have correlate d different meteorological quantities from the ECMWF model, such as convect ive precipitation and cloud top height, with ground-based lightning observa tions made during the EULINOX project. Convective precipitation gave the be st correlation for summer conditions over Europe. Using the established rel ationship between convective precipitation and lightning intensity, we have tested different vertical distributions of the NOx, lightning source in th e 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 POLI-NAT/SONEX campaigns. We found that a prescribed lightning NOx pr ofile gave the best agreement with the observations. The observations cover ed 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 i nsufficient spatial and temporal resolution, but under most other circumsta nces the new parameterisation performed reasonably well, and is a clear imp rovement over the previously used parameterisation based on cloud top heigh ts. (C) 2001 Elsevier Science Ltd. All rights reserved.