Seasonal and global NOx production by lightning estimated from the OpticalTransient Detector (OTD)

The Optical Transient Detector (OTD) lightning data for the 12-month period of 1996 are used to estimate the seasonal and global distributions of ligh tning-produced NOx. The relatively small viewing footprint and the low dete ction efficiency of the OTD sensor and other difficulties require extrapola tions of the OTD data to the actual global flash distributions. Furthermore , available measurements for the ratios of intracloud (IC) to cloud-to-grou nd (CG) flashes have been used to partition lightning counts for IC versus CG Bashes From the OTD observations. The resulting lightning distributions are then used to calculate the global and seasonal production of NOx, assum ing a NO production rate of 6.2 x 10(25) molecules for each CG flash and 8. 7 x 10(24) molecules for each IC flash. Consequently, we find that CG Bashe s produce more NOx than IC flashes despite fewer CG flashes by a factor of 3 or more, NOx production by lightning varies seasonally in accordance with the global lightning distribution, with the maximum production occurring i n the Northern Hemisphere in the local summer. The latitudinal distribution of NOx production exhibits a strong seasonal variation outside the tropics with the production occurring mainly in the summer hemisphere, whereas in the tropics the production is high throughout the year. The annual contribu tion to NOx production by lightning is higher in the Northern Hemisphere th an that in the Southern Hemisphere.