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?

Greenhouse Gas Scenarios

IPCC Fourth Assessment Report, 2007

Ozone-Depleting Substances

WMO-UNEP Scientific Assessment of Ozone Depletion, 2006

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

1980-2000 Ozone Change

1980-2000 Temp. Change

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)

Pacific SST

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)

Tropical vertical velocity

Age of Air

Impacts on tropical ozone

Impacts on total ozone (Jan)

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

4. Ozone Change in the 21st Century (C21)

What factors determine ozone change in the future?

Total Ozone in Jan & Oct

Pacific SST

Mean Age of Air

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

Tropical Ozone: 1960-2100

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

Antarctic O3 & T in GEOS CCM

∆O3

∆T

1999 - 1969 2094 - 2006 2094 - 2006

No Cl change

O3 & Climate: GEOS CCM

∆u

∆(SAM)

1999 - 1969 2094 - 2006

DJF Surface Pressure ChangesWith Chlorine

change

1999 - 1969

2094 - 2006

Without Chlorine change

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