Institute for Climate and Atmospheric Science SCHOOL OF EARTH AND ENVIRONMENT

1. Institute for Climate and Atmospheric Science SCHOOL OF EARTH AND ENVIRONMENT 3D SLIMCAT Studies of Arctic Ozone Loss Wuhu Feng Acknowledgments: Martyn Chipperfield, Stewart Davies, L. Gunn, V.L. Harvey, C.E. Randall, M.L. Santee, P.Ricaud, QUOBI and SCOUT-O3

2. OUTLINE • 3D CTM SLIMCAT • Examples of CTM results: Comparison with various measurements • Modelled O3 loss under different meteorology conditions • Sensitivity experiments • Conclusion

3. SLIMCAT/TOMCAT 3D CTM • Off-line chemical transport model with many different options. • Key points here: • Extends to surface using hybrid - (SLIMCAT), -p (TOMCAT). • Variable horizontal/vertical resolution. • Horizontal winds and temperatures from (UKMO, ECMWF etc) analyses • Model constrained to real meteorology--good for comparison with Obs. . • Vertical motion from diagnosed heating rates (SLIMCAT) or divergence of mass flux (TOMCAT). Note analysed vertical wind can be “noisy”. • 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 microphysical denitrification (DLAPSE) scheme included and detailed tropospheric chemistry scheme • Sequential chemical data assimilation scheme: sub-optimal Kalman Filter • http://www.see.leeds.ac.uk/slimcat

4. Comparison with MIPAS O3 in the SH Feng et al.(JAS, 2005)

5. Comparison with POAM O3 in the NH Singleton et al. (ACP,2005)

6. Long-term N2O variation Comparison with satellite and ground-based measurements Ricaud et al.(to be submitted)

7. Effect of chemical data assimilation Gunn et al.(to be submitted) • Assimilation of HALOE data (ie. CH4, O3, HCl and H2O) into SLIMCAT reproduce better long-term NO2 variations

8. Arctic Ozone loss versus VPSC New T42 run Obs New T15 run Old T15 run Chipperfield et al. (GRL, 2005) • First successful CTM simulation of seasonal O3 column loss and reproduces the past climate sensitivity of Arctic ozone depletion on T.

9. Modeled Arctic Ozone Loss Updated from Feng et al. (2007) • Year-to-year variations of ozone loss due to different meteorological conditions • 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

10. Sensitivity experiment • More ozone loss if the Arctic winter 2004/05 after late February was followed by 1997 and 2000 meteorological conditions • Arctic ozone loss would have been even more severe and complete loss would have occurred around late March if the winter 2004/05 was followed by 1997 conditions which had a record long-lasting cold polar vortex • No “Arctic ozone hole” structure if the winter 2004/05 followed by 2000 meteorological conditions. However, the “Arctic ozone hole” would have happened if followed by a spring like 1997 with a long-lasting cold polar vortex. Minimum temperature (K) at 456K from March to April for 2005, 2000 and 1997 from ECMWF analyses. (b) Maximum modelled local ozone loss (%) at 456 K for winter 2004/05 and two sensitivity runs where the simulation for 2004/05 was continued with meteorology for 1997 and 2000 after February 28. (c) As panel (b) but for minimum column O3 along with TOMS data for 2005 for any point poleward of 65o N. From Feng et al. (2007)

11. Laboratory Cl2O2 cross data Burkholder et al. (1990) JPL (2006) Huder and Demore (1995) Pope et al. (2007) L • Large discrepancy of cross section of Cl2O2 from laboratory measurements

12. Cl2O2 photolysis rate Burkholder et al. (1990) JPL (2006) Huder and Demore (1995) Pope et al. (2007) Burkholder et al. (1990) JPL (2006) Huder and Demore (1995) Pope et al. (2007) • Different Cross section of Cl2O2 results in different photolysis rate • JCl2O2 from recent new laboratory data is a factor of ~ 6 than the current JPL recommendation • Standard SLIMCAT CTM uses JCl2O2values based on Burkholder et al.(1990) data which is the fastest than other data

13. Impact of absorption cross section of laboratory Cl2O2on the modelling ozone loss 450 K for Antarctic 2003 475 K for Arctic 2002/03 Match Burkholder et al. (1990) JPL (2006) Huder and Demore (1995) Pope et al. (2007) Match Burkholder et al. (1990) JPL (2006) Huder and Demore (1995) Pope et al. (2007) • Ozone loss rate is very sensitive to JCl2O2 values • Similar evolutions of diagnosed ozone loss rate from model runs using different absorption cross section of Cl2O2 from laboratory measurements in the polar regions • Large discrepancy when using the new laboratory data (pope et al. 2007). Measurement problem or model still uncertain???

14. Impact of Cl2O2 cross section on the Arctic ozone loss • Large Arctic Ozone loss using different Cl2O2 cross section in model

15. Comparison with MKIV data MKIV Burkholder et al. (1990) JPL (2006) Huder and Demore (1995) Pope et al. (2007) • Standard SLIMCAT reproduces ClO very well while model using Pope et al. (2007) underestimated observed ClO ClO HCl ClONO2 O3

16. Chlorine partitioning Comparison with AURA MLS • SLIMCAT overestimate Chlorine activation? Need to test new PSC Scheme and ClOx kinetics Santee et al..(JGR, in press)

17. Best agreement for SLIMCAT with DLAPSE SLIMCAT overestimates chlorine activation, importance of Liquid aerosols in CTM

19. Summary and Outlook • Different measurements help testing simulations from CTM (ie. SLIMCAT), while the reliable model can be used to check the consistencies of the observations. • 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 • SLIMCAT reproduces the past climate sensitivity of Arctic ozone depletion on T • Recent new experiment shows large discrepancy of cross section of Cl2O2 from other laboratory measurements, which results in different photolysis rate • Ozone loss rate is very sensitive to JCl2O2 values • Standard SLIMCAT reproduces observed ozone loss rate quite well, while it underestimates ozone loss rate when using Pope et al. (2007) data. • SLIMCAT with detailed DLAPSE microphysical scheme is less denitrified while model with equilibrium scheme has stronger denitrification, however, there is only small effect on ozone loss between these two schemes. • Compare HIRDLS data (ie. O3, ClONO2, HNO3, CH4 etc) for available data period