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

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

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Ozone observations at ~30 km altitude above Ny-Ålesund

Model

solar max solar min solar max

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Decadal scale ozone anomalies

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Impact of energetic electrons?

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Ozone anomalies at Ny-Ålesund (79°N)

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Ozone anomalies at Neumayer / Antarktis (70°S)

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Ozone anomalies at South Pole

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Further evidence from SBUV (/2) satellite observations

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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.

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What is the evidence for electron precipitation?

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The geomagnetic Ap index:

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Is there an influence on total ozone during spring?

Ny-Ålesund

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Total ozone in spring largely controlled by Eliassen-Palm flux

Weber et al., 2003; Sinnhuber et al., 2004

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Does ozone in autumn influence EP flux in mid-winter?

Ny-Ålesund

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Ozone and EP flux: Southern hemisphere data

South Pole

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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.

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Current paradigm: EP flux controls polar temperatures

Newman et al., J. Geophys. Res., 2001

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Remember: Solar activity and QBO also play an important role

Labitzke and van Loon, 1990

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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.

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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.

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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?

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Acknowledgements

Sincere thanks to:

Miriam Sinnhuber

Peter von der Gathen, Markus Rex,

Gert König-Langlo, and Sam Oltmans

Mark Weber