1. 3D CTM Study of Arctic Ozone Loss and Denitrification Effect  Arctic ozone loss for 13 winters  DLAPSE Coupled to SLIMCAT  Denitrification effect on O3 loss Wuhu Feng, Martyn Chipperfield, Stewart Davies, V.L. Harvey, C.E. Randall School of Earth and Environment, University of Leeds, UK IASP, University of Colorado, Boulder, USA

2. Updated from Feng et al. (2007)

3. Chlorine Activation and denitrification Updated from Feng et al. (2007)

4. Modelled Arctic Ozone Loss  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  Arctic ozone loss would have more severe and continued if followed by a cold long-lasting polar vortex condition, such as 1997 Updated from Feng et al. (2007)

5.  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. Sensitivity experiments 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 65 o N. From Feng et al. (2007)

6. Denitrification effect

7. Comparison with AURA MLS data

8. Conclusion  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  Severe ozone loss occurred during Arctic winter 06/7 which is comparable to 04/5 and 1999/2000  Stronger denitrification in Arctic winter 2006/07  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.