Abstract
Abstract. 1-year data sets of monthly averaged nitrous oxide (N2O) and ozone (O3) derived from satellite measurements were used as a tool for the evaluation of atmospheric photochemical models. Two 1-year data sets, one solar occultation data set derived from the Improved Limb Atmospheric Spectrometer (ILAS and ILAS-II) and one limb sounding data set derived from the Odin Sub-Millimetre Radiometer (Odin/SMR) were employed. Here, these data sets are used for the evaluation of two Chemical Transport Models (CTMs), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and the Chemical Lagrangian Model of the Stratosphere (CLaMS) as well as for one Chemistry-Climate Model (CCM), the atmospheric chemistry general circulation model ECHAM5/MESSy1 (E5M1) in the lower stratosphere with focus on the Northern Hemisphere. Since the Odin/SMR measurements cover the entire hemisphere, the evaluation is performed for the entire hemisphere as well as for the low latitudes, midlatitudes and high latitudes using the Odin/SMR 1-year data set as reference. To assess the impact of using different data sets for such an evaluation study we repeat the evaluation for the polar lower stratosphere using the ILAS/ILAS-II data set. Only small differences were found using ILAS/ILAS-II instead of Odin/SMR as a reference, thus, showing that the results are not influenced by the particular satellite data set used for the evaluation. The evaluation of CLaMS, KASIMA and E5M1 shows that all models are in agreement with Odin/SMR and ILAS/ILAS-II. Differences are generally in the range of ±20%. Larger differences (up to −40%) are found in all models at 500±25 K for N2O mixing ratios greater than 200 ppbv, thus in air masses of tropical character. Generally, the largest differences were found for the tropics and the lowest for the polar regions. However, an underestimation of polar winter ozone loss was found both in KASIMA and E5M1 both in the Northern and Southern Hemisphere.
Highlights
The slowly decreasing level of halogens in the stratosphere in the coming decades is expected to lead to a gradual recovery from the chemical ozone depletion that is clearly noticeable in the extratropics since ∼ 1980 (WMO, 2007)
Analyses of chemical ozone loss in the polar regions in ChemistryClimate Model (CCM) simulations show a substantial underestimation of ozone loss in the Antarctic and a severe underestimation of ozone loss in the Arctic (Lemmen et al, 2006; Tilmes et al, 2007)
Hegglin and Shepherd (2007) showed that the variability of Arctic polar ozone loss is underestimated in the Canadian Middle Atmosphere Model (CMAM)
Summary
The slowly decreasing level of halogens in the stratosphere in the coming decades is expected to lead to a gradual recovery from the chemical ozone depletion that is clearly noticeable in the extratropics since ∼ 1980 (WMO, 2007). We use a method based on ozone (O3) and nitrous oxide (N2O) measurements to evaluate Chemical Transport Models (CTMs) as well as Chemistry Climate Models (CCMs) in the lower stratosphere In this method, monthly averages of the O3/N2O correlation binned by potential temperature are calculated. Hegglin and Shepherd (2007) proposed a further technique for using O3-N2O correlations to evaluate model results, namely, deriving equal area twodimensional Probability Density Functions (PDFs) of O3N2O pairs They applied this technique based on Atmospheric Chemistry Experiment (ACE-FTS) data to evaluate the aspects of transport and polar ozone loss in CMAM. A detailed description of the CLaMS model and this simulation can be found in McKenna et al (2002a,b), Konopka et al (2004) and Grooß et al (2005)
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