The global distribution of lightning NOx simulated on-line in a general circulation model

In this work, a time dependent lightning emission of nitrogen oxides is introduced in the LMDz general circulation model coupled to the chemistry module INCA using parameterizations for flash location and occurrence, lightning type, NO production per flash and vertical distribution. Major features of observed lightning activity are reproduced by the model as the seasonal cycle and the diurnal variation. Absolute simulated flash frequencies, however, are underestimated compared to observations from the Optical Transient Detector. Sensitivity studies are performed in order to better constrain the source of NOx by lightning. When the global lightning source is scaled to 5 TgN/yr, with vertical profiles specified according to Pickering et al. (1998), simulated concentrations of NO agree well with measurements made by Ridley et al. (1994) during the ELCHEM campaign. We confirm that lightning represents the main source of nitrogen in the tropical upper troposphere and contributes significantly to the total NOx field at northern midlatitudes in summer (20-30 percent). Aircraft emissions provide 5-35 percent of the total NOx in the upper troposphere at northern midlatitudes. (C) 2001 Elsevier Science Ltd. All rights reserved.