ON THE PRODUCTION OF ACTIVE NITROGEN BY THUNDERSTORMS OVER NEW-MEXICO

In July and August of 1989 the National Center for Atmospheric Researc h (NCAR) Sabreliner jet aircraft was used to probe electrically active and inactive convective storms over west central New Mexico to examin e the production of odd nitrogen in the middle and upper troposphere b y thunderstorms. In the anvil outflow or cloud top region of active an d nonactive storms, the majority of flights showed that O-3 was reduce d relative to the extracloud air owing to transport of ozone-poor air from lower altitudes. A similar result was found for active nitrogen ( NOx) and total odd nitrogen (NOy) in nonelectrically active storms, bu t the reduction in NOy was also enhanced by removal of soluble constit uents during convective transport. Examples of efficient removal from the gas phase are described. There was no evidence of O-3 production b y lightning discharges. Indeed, O-3 was a goad tracer over the lifetim e (similar to 1 hour) of the storms. During the active-to-mature stage of air mass thunderstorms, large enhancements in active nitrogen were observed in the anvil altitude region (9-11.8 km) and, in one case, i n the midlevel outflow (near 7 km) of a dissipating thunderstorm. Two thunderstorms allow good estimates of the NOx production by lightning within or transport to the upper altitude region (8-11.8 km). Thunders torms of August 12 and August 19 yield amounts in the range of 253-296 kg(N) and 263-305 kg(N), respectively. If, as an exercise, these amou nts are extrapolated to the global scale on the basis of the number of cloud-to-ground and intracloud lightning flashes counted or estimated for each storm and a global flash frequency of 100 s(-1) the result i s 2.4-2.7 and 2.0-2.2 Tg(N)/yr. Alternatively, an estimate for the two storms made on the basis of the average number of thunderstorms that occur per day globally (44,000) yields amounts in the range of 4.1-4.7 and 4.2-4.9 Tg(N)/yr, respectively. These estimates only apply to the production or transport of lightning generated NOx in or to the altit ude region between 8 km and the top of the thunderstorm anvil (similar to 11.8 km in these studies). Since in some large-scale models, light ning-generated NOx is equally distributed by mass into each tropospher ic layer, our estimates are roughly equivalent to those model runs tha t use a global source strength of about twice our estimate for the upp er altitude region. In several flights where the region below the base of thunderstorms was examined, no large enhancements in odd nitrogen which could be clearly attributed to lightning were observed. Apparent ly, the aircraft was not in the right place at the right time. Thus no estimate of the NOx production by lightning that remains below simila r to 8 km could be made.