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 http://www.env.leeds.ac.uk/slimcat
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.

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. Comparison with O3 sonde data10
Comparison with O3 sonde data
Pressure
100
Ny-Alesund 79oN 12oE
1000
Model gives a good simulation of O3, except overestimates the observations hPa.
Large O3 depletion between K with the largest ozone loss ~450K.
O3 (mPa)
700
Theta
550
500
450
400
350
300
O3 (vmr)
O3 loss

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

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 (Salawitch et al., GRL, 2005)
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)

12. Multi-annual T15 run from 01/01/1977
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.