Upper Atmosphere Research Satellite observations indicate that extensive denitrification without significant dehydration currently occurs only in the Antarctic during mid to late June. The fact that denitrification occurs in a relatively warm month in the Antarctic raises concern about the likelihood of its occurrence and associated effects on ozone recovery in a colder and possibly more humid future Arctic lower stratosphere. Polar stratospheric cloud lifetimes required for Arctic denitrification to occur in the future are presented and contrasted against the current Antarctic cloud lifetimes. Model calculations show that widespread severe denitrification could enhance future Arctic ozone loss by up to 30%.

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Abstract.We simulate accumulation of AleO3 particles in the atmosphere produced by solid-fueled rocket motors by using the Goddard Institute for Space

[1] The goal of this study is to show that trajectory hunting is an effective technique for comparison of multiplatform measurements. In order to achieve this goal, we (1) describe in detail the trajectory hunting technique (THT), (2) perform several consistency tests for THT (self-hunting and reversibility), (3) estimate uncertainties of this technique, and (4) validate THT results against those obtained by the traditional correlative analysis (TCA). THT launches backward and forward trajectories from the locations of measurements and finds air parcels sampled at least twice within a prescribed match criterion during the course of several days. TCA finds matched profiles for a chosen match criterion, averages them for each instrument separately, and compares the averaged profiles. As an example, we consider the 22 October to 30 November 1996 period in the Southern Hemisphere and compare the latest versions of relevant measurements made by the following five instruments: Microwave Limb Sounder (MLS, version 5 (v.5)), Halogen Occultation Experiment (HALOE, v.19), Polar Ozone and Aerosol Measurement II (POAM-II, v.6), Stratospheric Aerosol and Gas Experiment II (SAGE-II, v.6.1), and Improved Limb Atmospheric Spectrometer (ILAS, v.5.20). We present results for O 3 , H 2 O, CH 4 , HNO 3 , and NO 2 , which show that (1) ozone measurements from all five instruments agree to better than 0.4 (0.2) ppmv below (above) 30 km; (2) water vapor measurements agree within ±5-10% above 22 km; (3) methane measurements by HALOE and ILAS agree to better than 10% above 30 km with a possible positive offset of up to 10-15% by ILAS in the lower stratosphere; (4) MLS HNO 3 data corrected to account for some excited vibrational lines omitted in the v.5 HNO 3 retrieval agree with ILAS HNO 3 measurements to within $0.5 ppbv ($10-20%) over the range $450-750 K; (5) ILAS sunset NO 2 measurements are larger than both POAM-II and SAGE-II values by up to 10-15% below 30 km. The self-hunting tests show that the THT RMS noise is of the order of 1-2% for O 3 , CH 4 , and H 2 O and 4% for NO 2 and HNO 3 measurements in the stratosphere. Total THT-related uncertainties may be 3-5% for O 3 measurements when photochemical effects and sensitivities of the results to duration of trajectories and match criteria are taken into account. Good agreement is found between the THT and TCA results for each of these products and for each possible pair of instruments, with considerably better statistics (typically by at least an order of magnitude) in the THT case. This agreement validates the THT results.

Abstract. Severe and extensive denitrification, chlorine activation, and photochemical ozone loss were observed throughout the lower stratosphere in the 1999-2000 Arctic vortex. A large number of air parcels sampled between late February and mid-March, 2000, were photochemically intercomparable for chemical 03 loss rates. In these air parcels, the temporal evolution of the correlations of 0 3 with the NOy remaining after denitrification provides strong evidence for the role of NOy in moderating 03 destruction. In 71%-denitrified air parcels, a chemical 0 3 destruction rate of 63 ppbv/day was calculated, while in 43%-denitrified air parcels the destruction rate was only 43 ppbv/day. These observational results show that representative denitrification models will be required for accurate prediction of future Arctic 03 changes.