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| Titel |
OH populations and temperatures from simultaneous spectroscopic observations of 25 bands |
| VerfasserIn |
S. Noll, W. Kausch, S. Kimeswenger, S. Unterguggenberger, A. M. Jones |
| 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 ; 15, no. 7 ; Nr. 15, no. 7 (2015-04-01), S.3647-3669 |
| Datensatznummer |
250119611
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| Publikation (Nr.) |
 copernicus.org/acp-15-3647-2015.pdf |
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| Zusammenfassung |
| OH rotational temperatures are widely used to derive mesopause
temperatures and their variations. Since most data sets are only
based on a fixed set of lines of a single band, it is important to
know possible systematic uncertainties related to the choice of
lines. Therefore, a comprehensive study of as many OH bands as
possible is desirable. For this purpose, astronomical echelle
spectrographs at large telescopes are the most suitable instruments.
They offer a wide wavelength coverage, relatively high spectral
resolution, and high sensitivity. Moreover, since each ground-based
astronomical observation has an imprint of the Earth's atmosphere,
the data archives of large astronomical facilities are a treasure
for atmospheric studies. For our project, we used archival data of
the medium-resolution X-shooter echelle spectrograph operated by the
European Southern Observatory at Cerro Paranal in Chile. The
instrument can simultaneously observe all OH bands that are
accessible from ground. We reduced and analysed a set of 343
high-quality spectra taken between 2009 and 2013 to measure OH line
intensities and to derive rotational and vibrational temperatures of
25 bands between 0.58 and 2.24 μm. We studied the
influence of the selected line set, OH band, upper vibrational level
v′, and the molecular data on the derived level
populations and temperatures. The rotational temperature results
indicate differences by several degrees depending on the
selection. The temperatures for bands of even and odd v′ show
deviations which increase with v′. A study of the
temporal variations revealed that the nocturnal variability pattern
changes for v′ from 2 to 9. In particular, the spread of
temperatures tends to increase during the night, and the time of the
minimum temperature depends on v′. The vibrational temperatures
depend on the range of v′ used for their determination, since
the higher vibrational levels from 7 to 9 seem to be overpopulated
compared to the lower levels. The vibrational temperature tends to
increase during the night, while the intensity decreases. Our results
support the assumption that the OH emission altitude depends on
v′. Moreover, the emission layer appears to rise in the
course of the night, which makes the OH thermalisation less
efficient. The derived rotational temperatures and their change with
v′ seem to be significantly affected by non-equilibrium
populations. |
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