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Modeling of Stratospheric Ozone in the Climate System

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.

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Modeling of Stratospheric Ozone in the Climate System

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  1. 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

  2. Motivation How does climate change impact ozone? How does ozone change impact climate? 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

  3. Greenhouse Gas Scenarios IPCC Fourth Assessment Report, 2007

  4. Ozone-Depleting Substances WMO-UNEP Scientific Assessment of Ozone Depletion, 2006

  5. Outline of Presentation Application of the GEOS CCM to some questions involving ozone and climate (Goddard Earth Observing System Chemistry-Climate Model) Brief Description of GEOS CCM Stratospheric Ozone and Temperature: 1960-2005 Sensitivity to Sea-Surface Temperature: Past Ozone Change in the 21st Century (C21) Ozone Impacts on the Southern Hemisphere Climate Summary

  6. Brief Description of GEOS CCM A short overview of the model structure and the experiments performed

  7. 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

  8. 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 model • treats 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

  9. Model Experiments Observed Past Modeled 21st Century

  10. 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

  11. 1980-2000 Ozone Change

  12. 1980-2000 Temp. Change

  13. Value in 2000 Change from 1980 Ozone Temperature 90S-60S means Antarctic Ozone and Temp: Past • 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

  14. 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

  15. 3. Sensitivity to Sea-Surface Temperature: Past How different is the atmosphere when modeled SSTs are used in place of observations?

  16. SST: 1985-1994 Observed (HadISST) Simulated (HadGEM1) minus Observed (HadISST) Simulated (CCSM2) minus Observed (HadISST)

  17. Pacific SST

  18. 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)

  19. Tropical vertical velocity

  20. Age of Air

  21. Impacts on tropical ozone

  22. Impacts on total ozone (Jan)

  23. 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

  24. 4. Ozone Change in the 21st Century (C21) What factors determine ozone change in the future?

  25. Total Ozone in Jan & Oct

  26. Pacific SST

  27. Mean Age of Air

  28. 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

  29. Tropical Ozone: 1960-2100

  30. 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

  31. 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

  32. Ozone-Antarctic Climate: Past Changes,1969-1999 Ozone hole causes substantial seasonal circulation changes, in accord with prior observation- and model-based studies Change in surface pressure in DJF With Ozone Change No Ozone Change

  33. Antarctic O3 & T in GEOS CCM 1999 - 1969 2094 - 2006 2094 - 2006 ∆O3 ∆T No Cl change

  34. O3 & Climate: GEOS CCM 1999 - 1969 2094 - 2006 ∆u ∆(SAM)

  35. DJF Surface Pressure Changes With Chlorine change Without Chlorine change 1999 - 1969 2094 - 2006

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

  37. 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

  38. 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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