An assessment of Southern Hemisphere stratospheric NOx enhancements due totransport from the upper atmosphere

Data from the Halogen Occultation Experiment (HALOE) are used to evaluate t he contribution of upper atmospheric NOx to the stratospheric polar vortex. Using CH4 and potential vorticity as tracers, an isolated region of enhanc ed NOx is shown to occur in the Southern Hemisphere (SH) polar vortex almos t every spring from 1991-1996. The magnitude of this enhancement varies acc ording to the A(p) auroral activity index. Up to half of the NOx in the mid -stratospheric SH polar vortex may be due to particle precipitation. The pe ak enhancement occurred in 1991 with a magnitude of 3-5% of the NOy source due to N2O oxidation.