[1] The first simulations of stratospheric chemistry using the Chemical Lagrangian Model of the Stratosphere (CLaMS) are reported. A comprehensive chemical assimulation procedure is described that combines satellite, airborne, and balloon-borne tracer observations with results from a two-dimensional photochemical model simulation. This procedure uses tracer-tracer and tracer-potential vorticity mapping techniques. It correctly reproduces all basic features of the observed tracer distribution. This methodology is used to generate the initial composition fields that will be used for subsequent chemical simulations. Results from a 6-day simulation starting on 20 February 1997 show that the simulated HNO 3 distribution displays the correct morphology, although the extremes of the observed HNO 3 distribution are underestimated. The simulated ClO distribution exhibits a similar morphology to the observed Microwave Limb Sounder ClO distribution. Because of unseasonally low temperatures in the arctic lower stratosphere during spring 1997, high levels of chlorine activation are maintained in the simulation, resulting in up to 1.8 ppmv of chemical ozone loss over a 5-week period. Furthermore, simulations show strong spatially inhomogeneous chemical ozone depletion within the polar vortex and show that greatest ozone loss is confined to the vortex core. These results are confirmed by several Halogen Occultation Experiment and ozone sonde profiles, although the minimum ozone concentrations are overestimated. These studies demonstrate that CLaMS is capable of simulating vortex isolation, an essential feature of the polar vortex.

The Improved Limb Atmospheric Spectrometer (ILAS), a sensor for stratospheric ozone layer observation using a solar occultation technique, was mounted on the Advanced Earth Observing Satellite (ADEOS), which was put into a Sun‐synchronous polar orbit in August 1996. Operational measurements were recorded over high‐latitude regions from November 1996 to June 1997. This paper describes the data processing algorithm of Version 5.20 used to retrieve vertical profiles of gases such as ozone, nitric acid, nitrogen dioxide, nitrous oxide, methane, and water vapor from the infrared spectral measurements of ILAS. To simultaneously derive mixing ratios of individual gas species as a function of altitude, the nonlinear least squares method was utilized for spectral fitting, and the onion peeling method was applied to perform vertical profiling. This paper also discusses in detail estimation of errors (internal and external errors) associated with the derived gas profiles and compares the errors with repeatability. The internal error estimated from residuals in spectral fitting was generally larger than the repeatability, which suggests either that some unknown factors have not been incorporated into the forward model for simulating observed transmittance data or that some parameters in the model are inaccurate. The external error was almost comparable in magnitude to the repeatability. Numerical simulations were carried out to investigate performance of the nongaseous correction technique. The results showed that the background level of sulfuric acid aerosols has little effect on the retrieved profiles, while polar stratospheric clouds (PSCs) with extinction coefficients of the order of 10−3 km−1 at a wavelength of 780 nm have nonnegligible effects on the profiles of some gas species. Despite the problems that require further investigations, it is shown that the ILAS Version 5.20 algorithm generates scientifically useful products.

Abstract.Balloon

The ozone‐tracer correlation method is used to deduce the stratospheric ozone loss in the Arctic winter 1996–1997. Improvements of the technique are applied, such as a new calculation of the vortex edge [Nash et al., 1996] and an improved early vortex reference function. Winter 1996–1997 is characterized by a late formation and an unusually long lifetime of the polar vortex. Remnants of vortex air were found until May. Chemical ozone losses deduced from two satellite data sets, namely Improved Limb Atmospheric Spectrometer (ILAS) and Halogen Occultation Experiment (HALOE), are discussed. The ILAS observations allow a detailed analysis of the temporal evolution of the ozone‐tracer correlation inside the polar vortex and, in particular, of the development of the early vortex. For November and December 1996, it is shown that horizontal mixing still influences the ozone‐tracer relation. Significant PSC related chemical ozone loss occurred beginning at mid‐February, and the averaged column ozone loss is increasing toward the middle of May. From April onwards, ozone profiles in the vortex became more uniform. The decrease of ozone in the vortex remnants in April and May occurred due to chemistry. HALOE observations are available for March to May 1997. In the period 4–16 March 1997, the calculated ozone loss deduced from HALOE and ILAS is in good agreement. The average of the result from the two instruments is 15 ± 7 Dobson units (DU) inside the vortex core, in the altitude range of 450–550 K. At the end of March, a discrepancy between HALOE and ILAS ozone loss arises due to a significant difference (0.6 ppmv) between the two data sets in the relatively low ozone minimum measured at 475 K. Nonetheless, both data sets consistently show an inhomogeneity in ozone loss inside the vortex core at the end of March. The vortex is separated in two parts, one with a large ozone loss (HALOE 40–45 DU, ILAS 30–35 DU) and one with a moderate ozone loss (HALOE 15–30 DU, ILAS 5–25 DU) for 450–550 K. The ozone loss from HALOE in 380–550 K at that time was calculated to be 90–110 DU for the large ozone loss and 20–80 DU for the moderate ozone loss. The vortex average of column ozone loss from HALOE inside the vortex core at the end of March is 61 ± 20 DU, which is an increase of about 20% compared to the earlier study by Müller et al. [1997b] brought about by the improvement of the technique.

No abstract