1. How do Long-Term Changes in the Stratosphere Affect the Troposphere?
Mark P. Baldwin
Northwest Research Associates, Seattle, WA, USA
IAGA/ICMA/CAWSES Trends Workshop
St. Petersburg, Russia 9-13 September 2008

2. Outline
Stratospheric vortex variability affects the troposphere and weather.
Ozone loss has affected Antarctic climate.
Will increasing GHGs produce a trend in polar vortex strength?
Will increasing GHGs affect the variability of the stratosphere?
Ozone will recover, reversing the trend from the past ~25 years.

3. From Bill Randel
44-58 km
34-51 km
25-44 km
18-37 km
13-22 km

5. ODSs
Ozone

8. Northern Annular Mode (NAM)

9. Annular Modes – Latitudinal Profile

10. What are “annular modes?”
They are patterns that maximize variance
Not exactly annular in the troposphere
Close to annular in the stratosphere
Similar to North Atlantic Oscillation
Arctic Oscillation (AO), Northern & Southern Annular Mode (NAM, SAM)

11. Northern Annular Mode (NAM)
1000 hPa (Arctic Oscillation)
10 hPa
Annular mode patterns are similar from Earth’s surface to 50+km.

12. Composite surface maps for high and low AO index.
(From Thompson and Wallace, Science 2001)
>0.9°C

14. Annular Mode Terminology
Arctic Oscillation (AO): At or near Earth’s surface.
North Atlantic Oscillation (NAO): Very similar to AO, but more oriented to the Atlantic sector.
Northern Annular Mode (NAM): Same as the AO, but can describe higher levels in the atmosphere.
The surface NAM is the Arctic Oscillation.

15. Southern Hemisphere surface climate response to ozone depletion
Springtime ozone loss appears to drive changes in surface climate from late spring to summer.

16. Ozone Depletion

17. Simulated and observed geopotential height and temperature changes
Model results from Gillett & Thompson, Science 2003

18. Model results from Gillett & Thompson, 2003
Tropospheric changes
←SAM pattern
Model results from Gillett & Thompson, 2003

19. The lowest level is the AO index.
Weak Winds
Strong Winds
NAM index for 1998–1999.
The lowest level is the AO index.
From Baldwin and Dunkerton, Science 2001

20. Composites of strong and weak vortex events
Select strong events based only on the daily 10-hPa NAM index.
Form positive and negative composites.
Examine average behavior for the composites.

21. Time Delay
Long timescale
Baldwin and Dunkerton, 2001

22. Surface pressure anomalies after stratospheric events look like the Arctic Oscillation.
Baldwin and Dunkerton, 2001

23. Storm tracks during weak and strong regimes

24. Baldwin and Dunkerton, 2001

25. The Quasi-Biennial Oscillation (QBO)

27. The Equatorial Quasi-Biennial Oscillation
Baldwin et al., Reviews of Geophysics, 2001

28. Possible Dynamical Mechanisms
Direct effect of stratospheric wave driving and stratospheric temperature anomalies
Indirect effects involving waves:
-Effect on baroclinic waves/life cycles
-Effect on planetary-scale waves
Wave reflection in the stratosphere

29. The Future of the Stratosphere?
Increasing greenhouse gases cool the stratosphere.
Ozone recovery reverses cooling trends.
Stratospheric NAM index trend would depend on relative cooling of the polar cap.
Many (most?) models show a warmer, weaker NH vortex in winter.

30. IPCC: Altitude of the Model Top
Stratopause
Tropopause
Number of levels
Finally in relation to CO2 or greenhouse warming there is the vexatious question of the role of cloud.
GO THROUGH
To some extent the role of cloud depends on its height in the atmosphere. Low level cloud tends toward warming through long wave trapping, while high level cloud leads to cooling through solar radiation reflection
In our final slide today, lets briefly look at surface characteristics.
(IPCC slides from Eugene Cordero)

31. How Will Climate Change Affect Ozone Recovery?
Colder stratosphere slows ozone-depleting reactions.
Colder stratosphere increases PSCs; more ozone loss in spring.
Ozone recovery will not be a simple reversal of ozone depletion.

32. How will stratospheric change affect surface climate
How will stratospheric change affect surface climate? The answer depends on 1) trends in the strength of the polar vortex 2) future variability of the polar vortex

33. The Future of the Stratosphere?
Increasing greenhouse gases cool the stratosphere.
Ozone recovery reverses SH trends.
Stratospheric NAM index trend would depend on relative cooling of the polar cap.
Most models show a warmer, weaker NH vortex in winter and spring.

34. mark@nwra.com www.nwra.com/baldwin
Summary
Changes to the circulation of the lower stratosphere affect surface climate.
The future evolution of the stratosphere will depend on increasing GHGs, ozone changes, and changes to the troposphere.
We do not know how the stratosphere will change in the coming decades and centuries, and we do not know how surface climate will be affected.
We do not fully understand the dynamics of stratosphere- troposphere coupling.