Evidence for a thermospheric source of stratospheric NOx

Analyses of a three-year time series of rocket ozone measurements at Wallops Island, VA, a set of rocket ozone soundings across the Southern Hemisphere, and rocket soundings at Fort Churchill, Manitoba are reported. Evidence is obtained that the NOx budget is not simply explained by oxidation of biospheric nitrous oxide. I 1-D time-dependent photochemical model is used to compute the amount of NO2 required to maintain odd oxygen in a steady state after accounting for Chapman, odd hydrogen, and odd chlorine reactions. At Wallops Island, a mid-latitude station, the inferred seasonal variation of NOx is small with the fall and winter mixing ratios about 20 percent greater than the spring and summer values. The soundings at Fort Churchill require about the same NOx amount as at Wallops Island in the spring and summer months but more than twice this amount in late fall and winter. Results indicate that the nitrous oxide source of NOx is supplemented by a polar source during the fall and winter months. This is consistent with the descent of thermospheric air with its high nitric oxide content during the period of strong cooling in the polar night.