Stratospheric NOx enhancements in the southern hemisphere vortex in winter/spring of 2000

POAM III data show unusually large increases in stratospheric NO2 throughou t the late winter and spring at high southern latitudes during 2000. Using HALOE CH4 data as a tracer of vertical descent, we conclude that excess NOx was created by particle impacts in the upper atmosphere and descended in t he polar vortex during the winter. We speculate that these NOx enhancements were due to the solar proton event that occurred on 14-15 July 2000, and s how that they caused reductions of up to similar to 45% in middle stratosph eric ozone mixing ratios. Comparison of HALOE and POAM data in 2000 to data from 1991-1999 suggests that the 2000 NOx enhancements were the largest ev er documented by satellite in the southern hemisphere middle stratosphere. Also, based on H2O data, we conclude that NOx-enriched air observed in the south polar vortex from 1991-1999 originated in the mesosphere, not the the rmosphere as is often assumed.