1. Larger Chemical Ozone Loss in 2004/2005 Arctic Winter/Spring Wuhu Feng and Martyn Chipperfield School of Earth and Environment, University of Leeds Acknowledgments R. Salawitch, P. von der Gathen, H. Kuhlman et al Temperatures Modelled fields of ClO x, NOy, H 2 O etc. Modelled O 3 loss Comparison with previous years Comparison with ASUR data

2. Temperatures 04/05 v 99/00

3. Minimum Temperature – Cold winters since 95/96

4. SLIMCAT/TOMCAT 3D CTM Off-line 3D chemical transport model Extends to surface using hybrid  -  levels (SLIMCAT version). Horizontal winds and temperatures from ECMWF analyses. Vertical motion from diagnosed heating rates. Chemistry: ‘Full’ stratospheric chemistry scheme (41 species, 160 reactions) with heterogeneous chemistry on liquid/solid aerosols/PSCs and an equilibrium (NAT rock) denitrification scheme. Near real time run: 2.8 o x 2.8 o x 24 levels (0-60 km) Web page with results: http://www.env.leeds.ac.uk/slimcat

5. What has changed in model to improve polar O3? A lot! Key points for polar O 3 are probably: Updated kinetics (JPL 2002) + faster JCl 2 O 2 (Burkholder et al extended to 450 nm). NAT-based denitrification scheme. Minimum aerosol (H 2 SO 4 ) 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.

6. SLIMCAT 3D CTM – Arctic winters since 1994/95

7. SLIMCAT 3D CTM – Modelled dehydration

9. O 3 at Ny Alesund

10. SLIMCAT ClO x and NO y at Ny Alesund

11. SLIMCAT v ASUR Data 31/1/20055/2/2005 HCl ClO N2ON2O N2ON2O

13. Recent results (3/3/2000)

14. Conclusions (Updated) SLIMCAT model does a good job in simulation of polar ozone + related species for 2004/05 Arctic winter. ‘Largest modelled Arctic ozone loss so far’ for this time of year. Strongest modelled chlorine activation and much more descent than previous years Model captures the dehydration as measured on January 26 at (~67N, 27E)