Abstract

n global models of tropospheric ozone and oxidized nitrogen, it is usually assumed that cloud-to-cloud discharges are 3 to 10 × less effective than cloud-to-ground discharges in producing nitrogen oxides (NOx). This assumption is based on a limited number of observations and experiments regarding the acoustic and optical energy spectrum of lightning discharges. We claim that cloud-to-cloud and cloud-to-ground discharges dissipate similar amounts of energy and they may thereby be equally effective per discharge as NOx producers. Nevertheless, the mechanism of NOx production by electrical discharges still needs to be clarified, as well as whether there is a vertical differentiation in the production mechanism. We performed sensitivity studies with a global 3-D climatological tracer model (MOGUNTIA). The studies indicate that the simulated tropospheric distributions of oxidized nitrogen and ozone are sensitive to the vertical distribution of the lightning source assumed. Furthermore, it is shown that the strength of the global lightning source used in 3-D global model studies of oxidized nitrogen should be amplified by a factor of 2.6 if cloud-to-cloud discharges are equally effective as cloud-to-ground discharges in producing nitrogen oxides.