Kevin M. Grise David W.J. Thompson Department of Atmospheric Science Colorado State University

1. Dynamical Impacts of Antarctic Stratospheric Ozone Depletion on the Extratropical Circulation of the Southern Hemisphere Kevin M. Grise David W.J. Thompson Department of Atmospheric Science Colorado State University (Thanks also to Piers Forster) Chapman Conference on The Role of the Stratosphere in Climate and Climate Change Santorini, Greece September 25, 2007

2. Overview • Antarctic ozone hole is forcing trends in Southern Hemisphere circulation that are consistent with positive phase of Southern Annular Mode (SAM). • Idea: Because tropospheric trends resemble SAM, decompose these trends into component linearly congruent with SAM and residual component independent of SAM. • Goal: To assess relative contributions of dynamics and radiation in determining recent tropospheric temperature trends.

3. 1979-2001 Ozone Trends Pressure (hPa) Altitude (km) Randel and Wu (2007) Global Ozone Data Set

4. 1979-2001 NCEP-NCAR Reanalysis Trends Temperature (65°S - 90°S) Geopotential Height (65°S - 90°S) 1979: Satellite data first available for reanalysis 2001: Last year before 2002 sudden stratospheric warming

5. Understanding the Trends in the Troposphere (Thompson and Solomon 2002; Gillett and Thompson 2003) The trends in the troposphere possess a spatial pattern very similar to the Southern Annular Mode (SAM).

6. NCEP-NCAR Reanalysis Trend Decomposition T (65°S - 90°S) Z (65°S - 90°S) Total SAM Congruent Residual Contour Intervals: 0.5 K/decade 20 m/decade

7. HadSM3-L64 Model Trend Decomposition T (65°S - 90°S) Z (65°S - 90°S) Total SAM Congruent Residual Model Details: Gillett et al. (2003) Contour Intervals: 0.5 K/decade 20 m/decade

8. Can radiation explain residual trends? Temperature Trend Profiles for January (85°S) Solid: Temperature Dashed: Ozone Piers Forster Fixed Dynamical Heating NCEP-NCAR Reanalysis HadSM3-L64 Model

9. Transitioning to Sudden Warmings • Observed residual temperature trends in Antarctic summer troposphere are not replicated by HadSM3-L64 model and are unlikely to be caused by radiation changes from stratospheric ozone depletion. • A natural question to ask: Are residual temperature features observed in troposphere for stratospheric-tropospheric coupling associated with sudden stratospheric warmings?

10. Northern Hemisphere Sudden Warmings Decomposition T` (60°N - 90°N) Z` (60°N - 90°N) Total NAM Congruent Residual Data Source: NCEP-NCAR Reanalysis (1958-2001)(JFM) Contour Intervals: 0.15 K, 10 m

11. Preliminary Radiative Arguments Fixed Dynamical Heating Calculations for January (75°N) Piers Forster Horizontal Axis: Level where 10 DU ozone is added Vertical Axis: Temperature response due to enhanced longwave forcing

12. Conclusions • Recent stratospheric trends associated with ozone hole strongly project upon circulation of troposphere as positive phase of SAM. • SAM predominantly explains coupling of observed Z trends into troposphere but cannot account for observed T trends coupling to surface. • Small residual T features also exist for sudden warmings, particularly in upper troposphere. • Radiation could possibly explain residual T features associated with sudden warmings but cannot explain residual T trends in Antarctic summer troposphere.

13. Unanswered Questions • Can residual temperature features associated with sudden warmings be explained by radiation? • Do residual temperature features play any role in stratospheric-tropospheric coupling?

15. Robustness of 1979-2001 Temperature Trends Composite of 6 Antarctic Radiosonde Stations NCEP-NCAR Reanalysis (65°S - 90°S) Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC) (Free et al. 2005) Contour Interval: 0.5 K/decade

16. NCEP-NCAR Reanalysis Trend Decomposition: January T Z U Total SAM Congruent Residual Horizontal Axis: Latitude (South Pole  Equator) Contour Intervals: 0.25 K/decade, 20 m/decade, 0.5 (m/s)/decade

17. HadSM3-L64 Model Trend Decomposition: January T Z U Total SAM Congruent Residual Horizontal Axis: Latitude (South Pole  Equator) Contour Intervals: 0.5 K, 20 m, 0.5 m/s

18. Temperature Trend Profiles October (85°S) Solid: Temperature Dashed: Ozone Piers Forster Fixed Dynamical Heating NCEP-NCAR Reanalysis HadSM3-L64 Model

19. 10hPa NAM Regression Decomposition: Lag 0 T’ Z’ U’ Total NAM Congruent Residual Horizontal Axis: Latitude (Equator  North Pole) Contour Intervals: 0.05 K, 5 m, 0.25 m/s

20. 2002 Southern Hemisphere Sudden Warming Decomposition T` (65°S - 90°S) Z` (65°S - 90°S) Total SAM Congruent Residual Data Source: NCEP-NCAR Reanalysis Contour Intervals: 2 K, 75 m

21. Preliminary Radiative Arguments Fixed Dynamical Heating Calculations for January (75°S) Piers Forster

22. Radiatively Driven Mechanism Two Components: Radiative Trigger Component Internal Tropospheric Dynamics Component Ozone Hole Diabatic Cooling Anomalous eddy momentum fluxes act to reinforce poleward-shifted jet and prolong + SAM phase. (Lorenz and Hartmann 2001) Maximum baroclinic wave generation follows shift in jet. Reduced Downwelling Longwave Radiation Maximum dT/dy and jet shift poleward. z Surface Cooling y 90º S 30º S

23. Radiative Trigger Component 1979-2001 NCEP-NCAR Reanalysis Trends 200 hPa Temperature (65°S - 90°S) Downward Radiation Fluxes at Surface (65°S - 90°S)