Björn-Martin Sinnhuber Institute of Environmental Physics University of Bremen February 2006

1. Observed decadal scale changes in polar ozone suggest solar influence through energetic electron precipitation Björn-Martin Sinnhuber Institute of Environmental Physics University of Bremen February 2006

2. Ozone sonde observations at Ny-Ålesund (79°N)

3. Ozone observations at ~30 km altitude above Ny-Ålesund solar min solar max solar max Model

4. Decadal scale ozone anomalies

5. Impact of energetic electrons?

6. Ozone anomalies at Ny-Ålesund (79°N)

7. Ozone anomalies at Neumayer / Antarktis (70°S)

8. Ozone anomalies at South Pole

9. Further evidence from SBUV (/2) satellite observations

10. Summary of observed ozone changes: • Polar ozone in the mid-stratosphere during winter shows decadal changes of about 20%, much larger than can be explained by changes in solar UV changes alone. • The ozone changes occur more or less simultaneously over both hemispheres. • The correlation of the ozone anomalies with electron fluxes suggests precipitating energetic electrons as a possible mechanism.

11. What is the evidence for electron precipitation?

12. The geomagnetic Ap index:

13. Is there an influence on total ozone during spring? Ny-Ålesund

14. Total ozone in spring largely controlled by Eliassen-Palm flux Weber et al., 2003; Sinnhuber et al., 2004

15. Does ozone in autumn influence EP flux in mid-winter? Ny-Ålesund

16. Ozone and EP flux: Southern hemisphere data South Pole

17. Possible explanation for a relation between ozone and EP flux: • Ozone reduction at high latitudes leads to increased temperature contrast.(Reduced radiative heating) • Increased temperature gradient between mid and high latitudes alters propagation of planetary waves.(Change of refractive index) • Reduction of planetrary wave flux leads to further polar cooling and ozone loss.

18. Current paradigm: EP flux controls polar temperatures Newman et al., J. Geophys. Res., 2001

19. Remember: Solar activity and QBO also play an important role Labitzke and van Loon, 1990

20. Summary and concluions: There is an unexpectedly large decadal scale ozone variability in the winter polar stratosphere • The ozone changes occur more or less simultaneously over both hemispheres. • Proposed mechanism: Precipitation of energetic electrons can produce enhanced HOx and NOx in the mesosphere, leading to enhanced ozone loss. • The close correlation of ozone anomalies with observed electron fluxes at geo-stationary altitudes provides some evidence.

21. Summary and concluions (2): Possible impact on climate • We find an empirical correlation between mid-stratospheric ozone in early winter and total ozone and EP flux in late winter /spring. • If there is a direct link between early winter ozone anomalies and mid-winter EP flux this may provide a mechanisms for impact of solar variability on climate. • Finally, regardless of the possible underlying mechanisms, the observed correlation may offer some potential for long term weather forcasts.

22. Open questions: However, there are still a number of open questions: • How is the GOES electron flux related to the flux of precipitating electrons? • Is there any evidence for changes in HOx and/or NOx on decadal time scales? • What is the expected time lag between enhanced electron fluxes and reduced ozone? • Is there a relation between early winter ozone and mid-winter EP flux? Can models reproduce this mechanism?

23. Acknowledgements Sincere thanks to: • Miriam Sinnhuber • Peter von der Gathen, Markus Rex,Gert König-Langlo, and Sam Oltmans • Mark Weber