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Three-Dimensional Chemical Transport Model Studies of Arctic Ozone Depletion

Three-Dimensional Chemical Transport Model Studies of Arctic Ozone Depletion. Wuhu Feng and Martyn Chipperfield School of the Earth and Environment, University of Leeds. Model description Recent improvements to SLIMCAT 3D CTM Results Comparisons of new/old CTM for Arctic winter 2002/3

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Three-Dimensional Chemical Transport Model Studies of Arctic Ozone Depletion

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  1. Three-Dimensional Chemical Transport Model Studies of Arctic Ozone Depletion Wuhu Feng and Martyn Chipperfield School of the Earth and Environment, University of Leeds • Model description • Recent improvements to SLIMCAT 3D CTM • Results • Comparisons of new/old CTM for Arctic winter 2002/3 • Improved decadal simulations of Arctic O3 loss (Rex plot) • Conclusions Acknowledgments S. Davies, B. Sen, G. Toon, J.F. Blavier, C.R. Webster, C.M. Volk, A. Ulanovsky, F. Ravegnani, P. von der Gathen, H. Jost, E.C. Richard, H. Claude NERC, EU TOPOZ III, QUILT , QUOBI projects

  2. ARCTIC OZONE LOSS Measurements: colored squares Old SLIMCAT: black points Rex et al. (GRL,2004) Aim of the work 1: Quantify and understand the degree of chemical ozone loss Aim of the work 2: Improve the Chemical Transport Model (e.g. Rex plot)

  3. SLIMCAT/TOMCAT 3D CTM • Off-line chemical transport model [e.g. Chipperfield, JGR, 1999] • Extends to surface using hybrid - levels (SLIMCAT version). Variable horizontal/vertical resolution. • Horizontal winds and temperatures from analyses (e.g. UKMO, ECMWF (ERA-40 or operational)). • Vertical motion from diagnosed heating rates or divergence. • Radiation scheme MIDRAD or CCM scheme • Tropospheric physics: convection, PBL mixing etc. • Chemistry: ‘Full’ stratospheric chemistry scheme (41 species, 160 reactions) with heterogeneous chemistry on liquid/solid aerosols/PSCs and an equilibrium denitrification scheme. • NAT-based denitrification scheme included. www.env.leeds.ac.uk/slimcat

  4. 2002/03 Meteorology PSC extent decreases with height Very Low Temp. in Dec. 2002 (produces early O3 loss)

  5. NEW SLIMCAT VS OLD SLIMCAT comparison with MK4 balloon data CH4 N2O • Old SLIMCAT model (with lower boundary at 350K) overestimates N2O above 20 km. New version of SLIMCAT (which extends to the surface) gives better N2O distribution. • Different radiation schemes result in different transport (CCM better).

  6. 2) NEW SLIMCAT VS OLD SLIMCAT comparison with M55 aircraft data New version of SLIMCAT with CCM radiation scheme gives more (better) descent than MIDRAD radiation scheme in the old version of SLIMCAT N2O CH4

  7. 3) NEW SLIMCAT VS OLD SLIMCAT Comparison with O3 sonde data 425K Significant improvements in the new version of SLIMCAT (I.e. better representation of O3 in the lower stratosphere – better transport and better chemical loss) 460K 495K

  8. 4) NEW SLIMCAT VS OLD SLIMCAT comparison with POAM data OLD SLIMCAT Run NEW SLIMCAT Run 450K 450K Singleton et al., ACP(submitted),2004 • Significant improvements in the NEW SLIMCAT when compared with POAM satellite data (daily average in the vortex).

  9. New Model: Multiannual Simulations of Polar O3 Loss 2004 Observations 96 00 SLIMCAT – NEW 7.5o x 7.5o 95 93 96 97 SLIMCAT - OLD 94 03 98 99 1990 • New SLIMCAT reproduces the Rex plot much better

  10. New SLIMCAT: Vortex Averaged Profiles 1993-2000 for O3 (left) and O3 (right) C 1993 1994 550 C 1995 C 1996  Jan 15 Mar 25 SLIMCAT Obs. 400 Run OLD 0 4 1997 C 1998 W Profile of O3loss looks ok generally, even in warm winters. Model has larger changes near 550K. Model vortex-average does not get very low values of 2000. C 1999 2000 W

  11. What else has changed in model between old and new model? • A lot! Key points for polar O3 are probably: • Updated kinetics (JPL 2002) + faster JCl2O2 (Burkholder et al extended to 450 nm). • NAT-based denitrification scheme. • Minimum aerosol (H2SO4) loading. • Better vertical transport (more Cly in lower stratosphere) and no lower boundary near tropopause. • ECMWF analyses (ERA40 + operational). • Source gas scenarios: + 100pptv short-lived organic Cl, + shift in long-lived organic loading to shorter lived species.

  12. 1999/2000 Importance of model resolution 425K Higher resolution model produces large chemical ozone depletion, which agrees better with observations 460K 495K

  13. Effect of Resolution: New Model 1999/2000 Clyy (ppbv) NOy (ppbv) Op 2.8o x 2.8o 7.5o x 7.5o ERA 40 More denitrification at 2.8o x 2.8o Vortex maintains stronger gradients – more isolated

  14. Effect of Resolution: New Model ClOx (ClO + 2Cl2O2) (ppbv) Ny Alesund (79oN, 12oE) ERA40! 99/00 02/03 03/04 2.8o x 2.8o 7.5o x 7.5o

  15. Conclusion • Updated New SLIMCAT CTM now gives a good simulation of seasonal O3 column loss (and better January loss rates – not shown here). • Significant improvement in modelling of cold winters in mid 1990s – more modelled O3 loss. • Higher resolution (2.8o) does increase O3 loss especially in late winter/spring through maintaining active Cl for longer. • Importance of radiation scheme in the model: • Different radiation schemes used in the model can result in different transport and polar ozone loss. More sophisticated CCM scheme gives a better simulation than other schemes. • Chemical models/modules (based on tested/validated code) within CCMs can be expected to produce reasonable simulations of chemical polar O3 loss (under conditions so far experienced) – more positive than results of Rex et al (2004)!

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