UARS measurements of ClO and NO2 at 40 and 46 km and implications for the model ''ozone deficit''

We present the first diurnally-resolved measurements of ClO and NO2 at 3.1 and 1.4 hPa, approximately 40 and 46 km. Comparisons between the measurements of ClO and a zero-dimensional box model utilizing standard photochemistry and constrained by Upper Atmosphere Research Satellite (UARS) tracer measurements show that photochemical models overpredict ClO by a factor of two or more at 3.1 hPa and by a factor of 1.5-2.0 at 1.4 hPa. NO2 is well simulated by the model at 3.1 hPa, but systematically overestimated at 1.4 hPa. The model overestimate of ClO results in an overestimate of ozone loss in the upper stratosphere of 10-40%.