1. Sun-Climate Mechanisms Marvin A. Geller Stony Brook University Stony Brook, NY 11794-5000 Marvin A. Geller Stony Brook University Stony Brook, NY 11794-5000

2. I will be using the draft of the synthesis chapter that I wrote for Session 4 of the ISSI Workshop on Solar Variability and Planetary Climates that was held at ISSI on June 6-10, 2005, as the basis for this talk.

3. Session 4 1.Lennart Bengtsson - How does the climate respond to solar forcing? 2.William Ingram - Detection and attribution of climate change: understanding solar influence on climate. 3.Stefan Brönniman - Climate variability of the troposphere and lower stratosphere since the early 20 th century and its relation to solar variability. 4.Hauke Schmidt - The response of the atmosphere to solar forcing: a 3-D model study. 1.Lennart Bengtsson - How does the climate respond to solar forcing? 2.William Ingram - Detection and attribution of climate change: understanding solar influence on climate. 3.Stefan Brönniman - Climate variability of the troposphere and lower stratosphere since the early 20 th century and its relation to solar variability. 4.Hauke Schmidt - The response of the atmosphere to solar forcing: a 3-D model study.

4. Session 4 (continued) 5.Mark Baldwin - Stratosphere-troposphere coupling and annular modes. 6.Joanna Haigh - Solar influences on dynamical coupling between the stratosphere and troposphere. 7.Lesley Gray - A possible transfer mechanism for the 11-yr solar cycle to the lower atmosphere. 8.Kuniko Kodera - The role of dynamics in solar forcing. 9.Murry Salby - Influence of the solar cycle on the general circulation of the stratosphere and upper troposphere. 5.Mark Baldwin - Stratosphere-troposphere coupling and annular modes. 6.Joanna Haigh - Solar influences on dynamical coupling between the stratosphere and troposphere. 7.Lesley Gray - A possible transfer mechanism for the 11-yr solar cycle to the lower atmosphere. 8.Kuniko Kodera - The role of dynamics in solar forcing. 9.Murry Salby - Influence of the solar cycle on the general circulation of the stratosphere and upper troposphere.

5. Some Perspective We have already seen that the observed variations in total solar irradiance is on the order of 0.1 %, but that the solar spectral irradiance shows much larger variation at shorter wavelengths (including those crucial for ozone photochemistry). By what mechanism(s) can these solar variations produce the “observed” effects? We have already seen that the observed variations in total solar irradiance is on the order of 0.1 %, but that the solar spectral irradiance shows much larger variation at shorter wavelengths (including those crucial for ozone photochemistry). By what mechanism(s) can these solar variations produce the “observed” effects?

6. Bengtsson’s Paper - 1

7. Bengtsson’s Paper - 2

8. Bengtsson’s Paper - 3

9. Bengtsson’s Paper - 4

10. Bengtsson’s Paper - 5 1. In spite of a larger forcing at low latitudes the response is highest at higher latitudes. 2. Models which include a dynamical ocean model with sea-ice have different response than models that only include a mixed layer ocean. A full ocean model has very little warming at high latitudes of the Southern Hemisphere because of effective mixing of heat into the deep ocean. 3. Generally, different forcing agents are at first approximation additive and the overall global response is proportional to the sum of the globally average forcing 4. The pattern of response is uncorrelated to the pattern of forcing Climate response to forcing

11. Ingram - 1 Degeneracy “… the only thing we know about the best fit is that it has zero likelihood of being correct.”

12. Ingram - 2

13. Brönniman et al. - 1

14. Brönniman et al. - 2 “… from our analysis, we have some weak indications, but no firm evidence to assume that the solar signal in the upper tropospheric circulation is different in strength on the 11-year time scale than on the low-frequency time scale.”

15. Schmidt and Brasseur - 1

16. Schmidt and Brasseur - 2

17. Schmidt and Brasseur - 3

18. Baldwin - 1

19. Baldwin - 2

20. Baldwin - 3  Changes to the circulation of the lower stratosphere affect surface climate. This provides a possible mechanism to communicate a solar signal to Earth’s surface.  On climate-change timescales, we do not know how the stratosphere will change, and we do not know how surface climate will be affected.

21. Haigh and Blackburn - 1

22. Haigh and Blackburn - 2

23. Haigh and Blackburn - 3

24. Gray, Crooks, Palmer, Pascoe. and Sparrow - 1

25. Gray, Crooks, Palmer, Pascoe. and Sparrow - 2

27. Salby and Callaghan - 1

28. Salby and Callaghan (2005) then leave us with this intriguing causality scheme. 1.solar UV directly modulates upper stratosphere winds and temperatures (this is reasonably understood); 2.in some way, this solar UV modulates the QBO period (although research is progressing on this, this is not presently understood); 3.during winter months, the phase of the QBO modulates extratropical stratospheric planetary wave activity (work on this is proceeding, but we do not have a good understanding of this at present); 4.these variations in planetary wave activity modulate the occurrence of stratospheric warmings, which in turn strongly modulate the winter mean temperature and vortex strength this is reasonably well understood). Salby and Callaghan (2005) then leave us with this intriguing causality scheme. 1.solar UV directly modulates upper stratosphere winds and temperatures (this is reasonably understood); 2.in some way, this solar UV modulates the QBO period (although research is progressing on this, this is not presently understood); 3.during winter months, the phase of the QBO modulates extratropical stratospheric planetary wave activity (work on this is proceeding, but we do not have a good understanding of this at present); 4.these variations in planetary wave activity modulate the occurrence of stratospheric warmings, which in turn strongly modulate the winter mean temperature and vortex strength this is reasonably well understood).

29. Kodera - 1

30. Kodera - 2

31. Kodera - 3

32. Some Closing Thoughts 1.I haven’t discussed the cosmic ray/cloud modulation suggestions. There were papers by Curtius and Arnold on this at the ISSI Workshop. 2.I also haven’t discussed the suggestion of Meehl et al (2003) where small changes in solar insolation modulate tropical hydrology. 1.I haven’t discussed the cosmic ray/cloud modulation suggestions. There were papers by Curtius and Arnold on this at the ISSI Workshop. 2.I also haven’t discussed the suggestion of Meehl et al (2003) where small changes in solar insolation modulate tropical hydrology.

33. One New Result from Hameed and Lee (2005) - 1

34. One New Result from Hameed and Lee (2005) - 2