Transcript Three-Dimensional Chemical Transport Model Studies of Arctic Ozone Depletion

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
Improved decadal simulations of Arctic O3 loss (Rex plot)
• Conclusions
Acknowledgments
S. 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
ARCTIC OZONE LOSS
Measurements: colored squares
Old SLIMCAT: black points
Rex et al.
(GRL,2004)
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)
SLIMCAT/TOMCAT 3D CTM
• 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
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
N2O
CH4
 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).
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
425K
460K
495K
Significant improvements in
the new version of SLIMCAT
(I.e. better representation of
O3 in the lower stratosphere
– better transport and better
chemical loss)
4) NEW SLIMCAT VS OLD SLIMCAT comparison with POAM data
OLD SLIMCAT Run
450K
NEW SLIMCAT Run
450K
Singleton et al., ACP(submitted),2004
 Significant improvements in the NEW SLIMCAT when compared with POAM
satellite data (daily average in the vortex).
New Model: Multiannual Simulations of Polar O3 Loss
2004
Observations
96
00
95
SLIMCAT – NEW
7.5o x 7.5o
93
96
97
94
SLIMCAT - OLD
03
98
99
1990
 New SLIMCAT reproduces the Rex plot much better
New SLIMCAT: Vortex
Averaged Profiles
1993-2000 for O3 (left)
and O3 (right)
550
1995

Jan 15
Mar 25
C
1993
C
1994
1996
C
400
0
SLIMCAT
Obs.
Run
OLD
4
1997
C
1998
W
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.
1999
W
2000
C
What else has changed in model between old and new model?
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.
Importance of model resolution
1999/2000
425K
Higher resolution model
produces large chemical ozone
depletion, which agrees better
with observations
460K
495K
Effect of Resolution: New Model
Clyy (ppbv)
2.8o
x
2.8o
7.5o x 7.5o
1999/2000
NOy (ppbv)
Op
ERA 40
More denitrification at
2.8o x 2.8o
Vortex maintains stronger
gradients – more isolated
Effect of Resolution: New Model
ClOx (ClO + 2Cl2O2) (ppbv)
ERA40!
Ny Alesund (79oN, 12oE)
99/00
02/03
03/04
2.8o x 2.8o
7.5o x 7.5o
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)!