three-dimensional chemical transport model studies of arctic ozone depletion
DESCRIPTION
Three-Dimensional Chemical Transport Model Studies of Arctic Ozone Depletion. Wuhu Feng and Martyn Chipperfield School of the Earth and Environment, University of Leeds. Model description Recent improvements to SLIMCAT 3D CTM Results Comparisons of new/old CTM for Arctic winter 2002/3 - PowerPoint PPT PresentationTRANSCRIPT
Three-Dimensional Chemical Transport Model Studies of Arctic Ozone Depletion
Wuhu Feng and Martyn ChipperfieldSchool of the Earth and Environment, University of Leeds
AcknowledgmentsS. Davies, B. Sen, G. Toon, J.F. Blavier, C.R. Webster, C.M. Volk, A. Ulanovsky, F. Ravegnani, P. von der Gathen, H. Jost, E.C. Richard, H. Claude NERC, EU TOPOZ III, QUILT , QUOBI projects
• Model descriptionRecent improvements to SLIMCAT 3D CTM• ResultsComparisons of new/old CTM for Arctic winter 2002/3Improved decadal simulations of Arctic O3 loss (Rex plot) • Conclusions
Aim of the work 1: Quantify and understand the degree of chemical ozone loss
Aim of the work 2: Improve the Chemical Transport Model (e.g. Rex plot)
Measurements: colored squaresOld SLIMCAT: black points
Rex et al. (GRL,2004)
ARCTIC OZONE LOSS
• Off-line chemical transport model [e.g. 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.
Radiation scheme MIDRAD or CCM scheme
• 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.
www.env.leeds.ac.uk/slimcat
SLIMCAT/TOMCAT 3D CTM
2002/03 Meteorology
PSC extent decreases with height
Very Low Temp. in Dec. 2002(produces early O3 loss)
NEW SLIMCAT VS OLD SLIMCAT comparison with MK4 balloon data
Old SLIMCAT model (with lower boundary at 350K) overestimates N2O above 20 km. New version of SLIMCAT (which extends to the surface) gives better N2O distribution. Different radiation schemes result in different transport (CCM better).
N2O CH4
2) NEW SLIMCAT VS OLD SLIMCAT comparison with M55 aircraft data
New version of SLIMCAT with CCM radiation scheme gives more (better) descent than MIDRAD radiation scheme in the old version of SLIMCAT
N2O
CH4
3) NEW SLIMCAT VS OLD SLIMCAT Comparison with O3 sonde data
Significant improvements in the new version of SLIMCAT (I.e. better representation of O3 in the lower stratosphere – better transport and better chemical loss)
425K
460K
495K
OLD SLIMCAT Run NEW SLIMCAT Run
4) NEW SLIMCAT VS OLD SLIMCAT comparison with POAM data
Singleton et al., ACP(submitted),2004
Significant improvements in the NEW SLIMCAT when compared with POAM satellite data (daily average in the vortex).
450K450K
Observations
SLIMCAT - OLD
1990
2004
SLIMCAT – NEW7.5o x 7.5o
New Model: Multiannual Simulations of Polar O3 Loss
New SLIMCAT reproduces the Rex plot much better
99
98
03
97
93
95
96
00
9496
Jan 15Mar 25
SLIMCATObs.
Run OLD
Profile of O3 loss looks ok generally, even in warm winters.
Model has larger changes near 550K.
Model vortex-average does not get very low values of 2000.
1993
20001999
19981997
19961995
1994
C
C
C
C
C
W
W
400
550
40
New SLIMCAT: Vortex Averaged Profiles
1993-2000 for O3 (left) and O3 (right)
A lot! Key points for polar O3 are probably:
• Updated kinetics (JPL 2002) + faster JCl2O2 (Burkholder et
al extended to 450 nm).• NAT-based denitrification scheme.• Minimum aerosol (H2SO4) 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.
What else has changed in model between old and new model?
Importance of model resolution
Higher resolution model produces large chemical ozone depletion, which agrees better with observations
1999/2000
425K
460K
495K
2.8o x 2.8o
7.5o x 7.5o
1999/2000
Clyy (ppbv) NOy (ppbv)
More denitrification at 2.8o x 2.8o
ERA 40
Vortex maintains stronger gradients – more isolated
Op
Effect of Resolution: New Model
2.8o x 2.8o 7.5o x 7.5o
99/00
02/03
03/04
ClOx (ClO + 2Cl2O2) (ppbv) Ny Alesund (79oN, 12oE)ERA40!
Effect of Resolution: New Model
Conclusion• Updated New SLIMCAT CTM now gives a good simulation of seasonal O3
column loss (and better January loss rates – not shown here).
• Significant improvement in modelling of cold winters in mid 1990s – more modelled O3 loss.
• Higher resolution (2.8o) does increase O3 loss especially in late winter/spring through maintaining active Cl for longer.
• Importance of radiation scheme in the model:Different radiation schemes used in the model can result in different transport and polar ozone loss. More sophisticated CCM scheme gives a better simulation than other schemes.
• Chemical models/modules (based on tested/validated code) within CCMs can be expected to produce reasonable simulations of chemical polar O3 loss (under conditions so far experienced) – more positive than results of Rex et al (2004)!