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 Model solar max solar min solar max

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