modeling of stratospheric ozone in the climate system steven pawson gmao, nasa gsfc judith perlwitz...
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Modeling of Stratospheric Ozone in the Climate System
Steven PawsonGMAO, NASA GSFC
Judith PerlwitzCIRES, CU/NOAA ESRL
Richard S. StolarskiAtmospheric Chemistry & Dynamics Branch, NASA GSFC
Yung Group Caltech Lunchtime Seminar: March 18, 2008
Motivation
Can be tested with experiments using “chemistry-climate models” (CCMs) that couple chemistry with the circulation
Degree of feedback needed for understanding of ozone and climate
Impacts formulation of models used in IPCC climate assessments
How does climate change impact
ozone?
How does ozone change impact
climate?
Outline of Presentation
1. Brief Description of GEOS CCM
2. Stratospheric Ozone and Temperature: 1960-2005
3. Sensitivity to Sea-Surface Temperature: Past
4. Ozone Change in the 21st Century (C21)
5. Ozone Impacts on the Southern Hemisphere Climate
6. Summary
Application of the GEOS CCM to some questions involving ozone and climate
(Goddard Earth Observing System Chemistry-Climate Model)
1. Brief Description of GEOS CCM
A short overview of the model structure and the experiments performed
GEOS CCM, Version 1•GEOS-4 General Circulation Model: •Flux-form quasi-Lagrangian transport with material vertical coordinate (Lin, 2004)
•Gravity wave drag after Garcia and Solomon (1984)
•Sub-grid physics from NCAR CCM3 (Kiehl et al., 1998)
•Goddard stratospheric chemistry model•35 transported trace species•Family approach after Douglass and Kawa (1999)
•Reaction rates and cross sections from JPL evaluation 14
•Resolution (flexible)•2.5°×2° (longitude by latitude) •55 layers, with Δz≃1-1.5km in stratosphere
GCM-Chemistry Coupling•Solar radiation:
18 spectral bands covering the range 240nm – 450 µm
heating by O3, H2O, O2, and CO2 and cloud
effects•Longwave radiation:
Six-band modeltreats CO2, H2O, O3, CH4, N2O, CFC11, CFC12
•Gas distributions: Water: from moist physics in troposphere and modified by chemistry (methane oxidation) in stratosphere
CO2, other GHGs & CFCs: specify surface
concentrations from observations or future projected scenarios
Ozone: predicted by model in stratosphere and relaxed to zonal-mean climatology (Logan) in troposphere
Model ExperimentsName SST/ice
GHG (SRES)
CFCs (WMO)
Span
P1 HadISST Obs. Obs. 1950-2005
P2 HadISST Obs. Obs 1950-2005
P-Cl1960 HadISST Obs (1960 Cl)
1960 1950-2005
C21-CSST CCSM3 A1b Ab 2000-2099
C21-HSST HadGEM1 A1b Ab 2000-2099
C21-CSSTa CCSM2 A1b Ab 1970-2050
C21-HSSTa HadGEM1 A1b Ab 1970-2050
C21-Cl1960 CCSM3 A1b (1960 Cl)
1960 2000-2099
Observed
Modeled
Past
21st Century
2. Stratospheric Ozone and Temperature: 1960-2005
How did the atmosphere change in the recent past?
S. Pawson, R.S. Stolarski, A.R. Douglass, P.A. Newman, J.E. Nielsen, S.M. Frith, and M. Gupta (2008): Goddard Earth Observing System Chemistry-Climate Model Simulations of Stratospheric Temperature-Ozone Coupling between 1950 and 2005. J. Geophys. Res., in press
Antarctic Ozone and Temp: Past
Ozone
Temperature
Value in 2000 Change from 1980
90S-60S means
Ozone and temperature changes (1980-2000) in the GEOS CCM
• Observed SST (HadISST)
• IPCC GHG changes
• WMO/UNEP CFC emissions
• Green - P-Cl1960
• Red/blue - P1 and P2
• Purple - time slice runs
2. Stratospheric Ozone and Temperature: 1960-2005 - SUMMARY
How did the atmosphere change in the recent past?
Global ozone loss consistent with that detected in real atmosphere
Cooling of stratosphere - about half from ozone loss
Antarctic ozone hole leads to substantial temperature change
3. Sensitivity to Sea-Surface Temperature: Past
How different is the atmosphere when modeled SSTs are used in place of observations?
SST: 1985-1994
Observed (HadISST)
Simulated (HadGEM1) minus Observed (HadISST)
Simulated (CCSM2) minus Observed (HadISST)
Tropical 100-hPa Temp. (Jan)
P1 and P2 (Natural Variability)
C21-HSSTb and P1 (Impacts of cold SST)
C21-CSSTb and P1 (Impacts of better SST)
3. Sensitivity to Sea-Surface Temperature: Past
How different is the atmosphere when modeled SSTs are used in place of observations? - SUMMARY
Cold-biased SST leads to cold biased tropical upper troposphere (less diabatic heating)
Cold biased SST leads to decrease in tropical upwelling, with:
• Increase in mean age of air (global)
• More ozone in the tropical lower stratosphere
Antarctic Ozone: 1960-2100
Total ozone over Antarctica in October in six runs of the GEOS CCM, subject to CFC scenario Ab & IPCC GHG scenario A1b
4. Ozone Change in the 21st Century (C21)
What factors determine ozone change in the future? - SUMMARY
Tropical mean age and ozone show similar responses to lower SST (more ozone and older air)
Differences are large in the middle 21st Century but decrease near 2100 as SST differences converge
Antarctic ozone is dominated by CFC loading and interannual variability
5. Ozone Impacts on the Southern Hemisphere Climate
How does stratospheric ozone change impact the tropospheric circulation around Antarctica?
J. Perlwitz, S. Pawson, R. Fogt, J.E. Nielsen, W. Neff, The Impact of Stratospheric Ozone Hole Recovery on Antarctic Climate Change. Geophys. Res. Lett., in press
Ozone-Antarctic Climate: Past Changes,1969-1999
With OzoneChange
No Ozone
Change
Change in surface pressure in DJF
Ozone hole causes substantial seasonal circulation changes, in accord with prior observation- and model-based studies
Comparison: AR4 C21 Models
GEOS CCM, fixed Cl
GEOS CCM
AR4 models, withno ozone recovery
AR4 models, withozone recovery
5. Ozone Impacts on the Southern Hemisphere Climate
How does stratospheric ozone change impact the tropospheric circulation around Antarctica? -
SUMMARY
Strong seasonal anomaly in SH circulation that peaks when ozone hole is strongest
Springtime ozone loss leads to strong positive SAM anomaly (stronger westerly winds) in summertime
GHG change causes a similar year-round response that increases through 21st Century
Ozone impact decreases through 21st Century
Summary
GEOS CCM shows expected stratospheric response to CFC and GHG loadings
Temperature response to ozone change is on the low end of simulated responses
SST biases have a strong, direct impact on upwelling in the tropical low stratosphere and ozone
Stratospheric ozone change in the C21 is dominated by SST change (GHG) in the Tropics and by interannual variability at high latitudes
Seasonal changes in Antarctic circulation are dominated by the summertime response to the ozone hole
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