Evidence for a Thermospheric Source of Stratospheric NOX

Abstract

Analysis 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 has produced evidence that the NOx budget is not simply explained by oxidation of biospheric nitrous oxide. A 1-D time-dependent photochemical model is used to compute the amount of NOx required to maintain odd oxygen in a steady state after accounting for Chapman, odd hydrogen, and odd chlorine reactions. The ozone and air densities and the air temperature are measured quantities which are fixed during the calculations. At Wallops Island, a mid-latitude station, the inferred seasonal variation of NOx is small with the fall and winter mixing ratios about 20% 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 double this amount in late fall and winter. The latitude dependence of NOx, derived from the fall season southern hemisphere ozone data, requires a decrease from the equator to midlatitudes, followed by an increase at higher latitudes. These combined 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 therrao- spheric air with its high nitric oxide content during the period of strong cooling in the polar night.