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| Titel |
Geomagnetic activity related NOx enhancements and polar surface air temperature variability in a chemistry climate model: modulation of the NAM index |
| VerfasserIn |
A. J. G. Baumgaertner, A. Seppälä, P. Jöckel, M. A. Clilverd |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 9 ; Nr. 11, no. 9 (2011-05-12), S.4521-4531 |
| Datensatznummer |
250009717
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| Publikation (Nr.) |
 copernicus.org/acp-11-4521-2011.pdf |
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| Zusammenfassung |
| The atmospheric chemistry general circulation model ECHAM5/MESSy is used to
simulate polar surface air temperature effects of geomagnetic activity
variations. A transient model simulation was performed for the years
1960–2004 and is shown to develop polar surface air temperature patterns
that depend on geomagnetic activity strength, similar to previous studies. In
order to eliminate influencing factors such as sea surface temperatures (SST)
or UV variations, two nine-year long simulations were carried out, with
strong and weak geomagnetic activity, respectively, while all other boundary
conditions were held to year 2000 levels. Statistically significant
temperature effects that were observed in previous reanalysis and model
results are also obtained from this set of simulations, suggesting that such
patterns are indeed related to geomagnetic activity. In the model, strong
geomagnetic activity and the associated NOx (= NO + NO2)
enhancements lead to polar stratospheric ozone loss. Compared with the simulation with weak
geomagnetic activity, the ozone loss causes a decrease in ozone radiative
cooling and thus a temperature increase in the polar winter mesosphere.
Similar to previous studies, a cooling is found below the stratopause, which
other authors have attributed to a decrease in the mean meridional
circulation. In the polar stratosphere this leads to a more stable vortex. A
strong (weak) Northern Hemisphere vortex is known to be associated with a
positive (negative) Northern Annular Mode (NAM) index; our simulations
exhibit a positive NAM index for strong geomagnetic activity, and a negative
NAM for weak geomagnetic activity. Such NAM anomalies have been shown to
propagate to the surface, and this is also seen in the model simulations. NAM
anomalies are known to lead to specific surface temperature anomalies: a
positive NAM is associated with warmer than average northern Eurasia and
colder than average eastern North Atlantic. This is also the case in our
simulation. Our simulations suggest a link between geomagnetic activity,
ozone loss, stratospheric cooling, the NAM, and surface temperature
variability. Further work is required to identify the precise cause and effect of the coupling between these regions. |
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