Sensitivity Studies of Ozone Depletion with a 3D CTM

1. Sensitivity Studies of Ozone Depletion with a 3D CTM Wuhu Feng1, M.P. Chipperfield1, S. Dhomse1, L. Gunn1, S. Davies1, B. Monge-Sanz1, V.L. Harvey2, C.E. Randall2, M.L. Santee3 1. School of Earth and Environment, University of Leeds, U.K. 2. LASP, University of Colorado, Boulder, U.S.A. 3. JPL, California Institute of Technology, Pasadena, California , U.S.A. earfw@env.leeds.ac.uk 1. Introduction 3D CTMs and CCMs have been widely used to study the dynamical and chemical processes which control polar ozone losses and mid-latitude ozone trends. However, there are still some uncertainties in both the models and our understanding. In this poster, a number of model experiments are used to discuss some of these uncertainties. We show the modelled Arctic ozone loss under different meteorological conditions (Fig.1) and discuss the denitrification effect on the Arctic ozone loss (Fig.2) and the impact of different absorption cross section of Cl2O2 (Fig. 3) . Model transport issues are discussed by running the CTM with options of assimilation of long-lived traces (HALOE CH4, O3, HCl and H2O from 1991-2002) (Fig. 4, 5) and by using the new ERA-Interim 4D-var reanalyses (1989-1998) (Fig 6). 2. SLIMCAT 3D CTM • 3D off-line chemical transport model forced by meteorlogical analyses. • - vertical coordinate. • Detailed chemical scheme. • Chemical data assimilation scheme • Different treatment of PSCs: (i) equilibrium denitrification scheme or (ii) detailed DLAPSE microphysical scheme. 3.1 Modelled Ozone Loss Under Different Meteorological Conditions . 3.3 Cl2O2 Photolysis • Arctic ozone loss is initially limited by the availability of sunlight in early winter and curtailed by the breakdown on the vortex in late winter/spring. • Year-to-year variations of polar Arctic O3 loss due to different meteorological conditions. Fig 1. Time series of vortex-averaged model chemical ozone loss for 456 K (%) for simulations of 14 Arctic winters. Also shown is the accumulated daily relative sunlit area north of 66oN geographic latitude integrated since December 1 (sza 93o) in units of relative area days (circles, right axis). Fig 3.Impact of different laboratory measurements (Burkholder et al. (1990), JPL (2006), Huder and Demore (1995) and Pope et al. (2007)) of Cl2O2 absorption cross section on the polar ozone loss rate at 475 K for Arctic winter 2002/03. 3.2 Denitrification Effect on Arctic Ozone Loss • Modelled O3 loss is sensitive to the • absorption cross sections of Cl2O2 • Applying the new cross section from Pope et al. (2007) in the model leads to large discrepancy and very poor agreement with observations. Fig 2. Comparisons of HNO3 and ClO from AURA MLS measurements and simulations using different PSC schemes (equilibrium, DLAPSE and no sedimentation) and without chlorine activation and N2O5+H2O reaction on liquid aerosols at 456 K and their impact on Arctic ozone loss. • SLIMCAT with detailed DLAPSE scheme is less denitrified than using equilibrium scheme and better reproduces observed HNO3. • Basic (equilibrium) model overestimates chlorine activation (MLS ClO). Reducing the denitrification and chlorine activation on aerosols can improve the comparisons somewhat. 3.5 Effect of Meteorological Analyses 3.4 Effect of Chemical Data Assimilation Fig 4. CH4 zonal mean for July 1992 from SLIMCAT runs with/without assimilation of HALOE data. Fig 6. Comparisons of ozonesonde observations at Resolute (75N) with SLIMCAT results using ERA-40 and ERA-Interim meteorological analyses . • SLIMCAT forced by ERA-40 and Interim analyses captures observed O3 seasonal cycle quite well. • The smaller O3 values from ERA-Interim run are in better agreement with the observations. • SLIMCAT with data assimilation shows an increased CH4 gradient in the subtropics. • SLIMCAT run with assimilation produces much better long-term NO2 variations than the basic model run. • Long-lived tracer assimilation ‘corrects’ transport errors. This work was supported by the EU SCOUT-O3 project. The ECMWF analyses were obtained via the British Atmospheric Data Centre. Chipperfield, M.P. , JGR, 104, 1781-1805, 1999. Feng W., et al., ACP, 7, 2357-2369, 2007. Feng W, et al, GRL, doi:10.1029/2006GL029098,2007. Fig 5. Ground-based column NO2 at Lauder comparison with SLIMCAT runs with/without assimilation of HALOE CH4, H2O, HCl and O3.