Modeling of Stratospheric Ozone in the Climate System Steven Pawson GMAO, NASA GSFC Judith Perlwitz CIRES, CU/NOAA ESRL Richard S. Stolarski Atmospheric 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: 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 Δ z ≃ 1-1.5km in stratosphere

GCM-Chemistry Coupling Solar radiation:  18 spectral bands covering the range 240nm – 450 µm  heating by O 3, H 2 O, O 2, and CO 2 and cloud effects Longwave radiation:  Six-band model  treats CO 2, H 2 O, O 3, CH 4, N 2 O, CFC11, CFC12 Gas distributions:  Water: from moist physics in troposphere and modified by chemistry (methane oxidation) in stratosphere  CO 2, 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 Experiments NameSST/ice GHG (SRES) CFCs (WMO) Span P1HadISSTObs P2HadISSTObs.Obs P-Cl1960HadISST Obs (1960 Cl) C21-CSSTCCSM3A1bAb C21-HSSTHadGEM1A1bAb C21-CSSTaCCSM2A1bAb C21-HSSTaHadGEM1A1bAb C21-Cl1960CCSM3 A1b (1960 Cl) Observed Modeled Past 21st Century

2. Stratospheric Ozone and Temperature: 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 J. Geophys. Res., in press

Ozone Change

Temp. Change

Antarctic Ozone and Temp: Past Ozone Temperature Value in 2000Change from  S-60  S means Ozone and temperature changes ( ) 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: 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: 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: Total ozone over Antarctica in October in six runs of the GEOS CCM, subject to CFC scenario Ab & IPCC GHG scenario A1b

Tropical Ozone:

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, With Ozone Change 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 O 3 & T in GEOS CCM ∆O 3 ∆T No Cl change

O 3 & Climate: GEOS CCM ∆u ∆(SAM)

DJF Surface Pressure Changes With Chlorine change Without Chlorine change

Comparison: AR4 C21 Models GEOS CCM, fixed Cl GEOS CCM AR4 models, with no ozone recovery AR4 models, with ozone 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