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| Titel |
Resonance scattering by auroral N2+: steady state theory and observations from Svalbard |
| VerfasserIn |
O. Jokiaho, B. S. Lanchester, N. Ivchenko |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 27, no. 9 ; Nr. 27, no. 9 (2009-09-04), S.3465-3478 |
| Datensatznummer |
250016642
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| Publikation (Nr.) |
 copernicus.org/angeo-27-3465-2009.pdf |
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| Zusammenfassung |
| Studies of auroral energy input at high latitudes often depend on
observations of emissions from the first negative band of ionised
nitrogen. However, these emissions are affected by solar resonance
scattering, which makes photometric and spectrographic
measurements difficult to interpret. This work is a statistical
study from Longyearbyen, Svalbard, Norway, during the solar
minimum between January and March 2007, providing a good coverage
in shadow height position and precipitation conditions. The High
Throughput Imaging Echelle Spectrograph (HiTIES) measured three
bands of N2+ 1N (0,1), (1,2) and (2,3), and one N2 2P band
(0,3) in the magnetic zenith. The brightness ratios of the N2+
bands are compared with a theoretical treatment with excellent
results. Balance equations for all important vibrational levels of
the three lowest electronic states of the N2+ molecule are
solved for steady-state, and the results combined with ion
chemistry modelling. Brightnesses of the (0,1), (1,2) and (2,3)
bands of N2+ 1N are calculated for a range of auroral electron
energies, and different values of shadow heights. It is shown that
in sunlit aurora, the brightness of the (0,1) band is enhanced,
with the scattered contribution increasing with decreasing energy
of precipitation (10-fold enhancements for energies of 100 eV).
The higher vibrational bands are enhanced even more significantly.
In sunlit aurora the observed 1N (1,2)/(0,1) and (2,3)/(0,1)
ratios increase as a function of decreasing precipitation energy,
as predicted by theory. In non-sunlit aurora the N2+ species
have a constant proportionality to neutral N2. The ratio of
2P(0,3)/1N(0,1) in the morning hours shows a pronounced decrease,
indicating enhancement of N2+ 1N emission. Finally we study
the relationship of all emissions and their ratios to rotational
temperatures. A clear effect is observed on rotational development
of the bands. It is possible that greatly enhanced rotational
temperatures may be a signature of ion upflows. |
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