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| Titel |
Investigation of the HDO/H2O ratio on Venus from SOIR solar occultations on board Venus Express |
| VerfasserIn |
H. Matsui, A. Mahieux, S. Robert, V. Wilquet, R. Drummond, A. C. Vandaele, N. Iwagami, J.-L. Bertaux |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250062089
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| Zusammenfassung |
| The SOIR instrument performs solar occultation measurements in the IR region (2.2 - 4.3
μm) at a resolution of 0.12 cm-1, the highest on board Venus Express. It combines an
echelle spectrometer and an AOTF (Acousto-Optical Tunable Filter) for the order
selection.
The wavelength range probed by SOIR allows a detailed chemical inventory of the Venus
atmosphere at the terminators in the upper mesosphere and lower thermosphere (70 to 170
km) with an emphasis on vertical distribution of the gases. H2O and HDO have been
routinely monitored at various latitudes of the Venus terminator, using the temperature
profiles obtained from the SOIR CO2 density profiles. The HDO/H2O ratios are obtained
from an altitude region extending from 70 km up to 100 km, and show a vertical
gradient.
Observations made at the IRTF telescope in Hawaii in 2010 showed a disk-averaged
mixing ratio of HDO is 0.22 ± 0.03 ppm for a representative height region of 62-67 km.
Based on many previous H2O measurements, the HDO/H2O ratio is found to be
140 ± 20 times larger than the telluric ratio. This lies between the ratios of 120
± 40 and 240 ± 25, respectively, reported for the 30-40 km region [De Bergh et
al. 1991] by ground-based night-side spectroscopy and for the 80-100 km region
by solar occultation measurement on board the Venus Express [Fedorova et al.
2008].
In addition to this, past observations at an altitude of 70 km show that HDO on Venus in
the early evening shows a latitudinal structure, and HDO mixing ratio at higher latitude is two
times larger that in the lower latitude regions. So there is probably a vertical distribution
or/and a latitudinal structure.
From measurements obtained by SOIR on Venus Express at the Venus terminator, the
D/H ratio seems to be very variable, and we confirm that the D/H ratio is larger at higher
altitude. |
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