3D CTM Study of Polar and Mid-Latitude Ozone Depletion and Climate Change

1. 3D CTM Study of Polar and Mid-Latitude Ozone Depletion and Climate Change Wuhu Feng and Martyn Chipperfield School of Earth and Environment,University of Leeds, U.K. • Updated 3D CTM SLIMCAT (Recent improvements to the model) • Polar Ozone Loss (2004/05 Arctic winter compared with previous winters) • Mid-Latitudes Ozone change (Sensitivity Experiments of BrO Chemistry) • Conclusions Acknowledgments Supported by NERC and SCOUT-O3 projects

2. SLIMCAT/TOMCAT 3D CTM • Off-line chemical transport model [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. • 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. http://www.env.leeds.ac.uk/slimcat

3. Updated 3D CTM: Arctic Ozone loss versus VPSC New T42 run Obs New T15 run Old T15 run Chipperfield et al.(GRL, 2005) • Linear relationship between ozone loss and PSC volume; • First successful CTM simulation of seasonal O3 column loss • and reproduces the past climate sensitivity of Arctic ozone depletion on T.

4. Record-Observed Arctic Ozone Loss in 04/05 Winter Quirin Schiermeier (Nature,2005) The Largest Arctic ozone losses observed in 2004/2005

5. Cold Meteorological Conditions in 2004/2005 Arctic Winter PSC Area Minimum Temperature • Large Area of PSC formation as result of very low temperatures.

6. Unusual polar vortex in 2004/2005 Arctic winter Comparison of SLIMCAT runs for past 11 years (ECMWF analyses) 493K 456K • Largest Polar Vortex since late January in 2004/2005 Arctic winter.

7. Large PSC Occurrence in 2004/2005 Arctic Winter 456K 493K • Largest NAT PSC area from late January in 2004/5 • Largest Ice PSC area since late January in 2004/2005 Arctic winter.

8. 10 Comparison with O3 sonde data Pressure 100 Ny-Alesund 79oN 12oE • Model gives a good simulation of O3, except overestimates the observations 300-100 hPa. • Large O3 depletion between 400-650K with the largest ozone loss ~450K. 1000 O3 (mPa) 700 Theta 550 500 450 400 350 300 O3 loss O3 (vmr)

9. Comparison with O3 sonde data • SLIMCAT reproduces the increase in December ozone and also reproduces the large decline of ozone mixing ratio from January to the mid-March. Passive O3 Chemical loss

10. O3 Loss at 456K Partial Column O3 Loss Near-record large O3 loss in 2004/2005 Fast deactivation in March than 99/00

11. CTM BrO problem Stratospheric bromine supplied by decomposition of VSL (very short lived) organics not considered in most global models as well as tropospheric BrO (Salawitch et al., GRL, 2005) (Salawitch et al., GRL, 2005)

12. BrO Experiment • Multi-annual T15 run from 01/01/1977 • Forced by ECMWF analyses (ERA40+Operational) • Exp336: Basic SLIMCAT run with new Bry • EXP337:as EXP336 but with fixed halogen • EXP338:as EXP336 but without the extra bromine species (about 6 pptv less Bry)

13. Long-term Column Ozone Comparison (1978-2004) • Model captures the observed year-to-year variability • Low Tropical column O3, and too large O3 in the mid and higher latitude

14. Anomaly Mid-lat column ozone comparison 35N-60N 60S-35S Fixed Halogen Fixed Halogen Basic Run Basic Run • Model reproduce the observed decrease of mid-latitude column ozone, but large discrepancy occurred in 1988 and 1993. • Large effect of BrO chemistry in the mid-latitude ozone change

15. Conclusions • Updated New SLIMCAT CTM now gives a good simulation of seasonal O3 column loss • Near-record Arctic ozone loss in 2004/2005 due to much more chlorine activation occurring on the largest surface areas of polar stratospheric clouds (PSCs) inside the polar vortex at very low temperatures, • However, less chlorine activation on PSCs in March 2005 than 2000 slowed down further chemical ozone loss in the late spring. • Stratospheric bromine supplied by decomposition of VSL has been added in SLIMCAT and has important effect on mid-latitude ozone trends.