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