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| Titel |
Water Vapour Abundance and Distribution in the Lower Venusian Atmosphere |
| VerfasserIn |
S. Chamberlain, J. Bailey |
| 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 |
250061081
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| Zusammenfassung |
| We present ground-based observations and modelling studies of water vapour abundance and
distribution in the Venusian lower atmosphere through analysis of absorption band depths
within the 1.18 μm window.
The lower atmosphere of Venus is difficult to study by both in situ and remote
instruments. This is due to the planet wide cloud cover that obscures visual wavelengths and
surface pressures approaching 100 times that of the Earth. In 1984 ground based observations
resulted in the discovery of atmospheric windows on the Venusian nightside (Allen and
Crawford, 1984). Here, near infrared radiation originating at the surface and lower
atmosphere, pass relatively unimpeded through the Venus clouds. This discovery enabled
remote studies of the Venusian subcloud region.
Determining the abundance and distribution of water vapour is key to understanding the
development, maintenance and links between major radiative and dynamical features of the
Venus atmosphere. Water vapour in the lower atmosphere plays an important role in heat
transfer and is pertinent to the runaway greenhouse effect and dynamical superrotation
observed on Venus. Detailed studies of water vapour abundance and distribution throughout
the lower atmosphere of Venus are therefore needed in order to develop accurate chemical,
radiative and dynamical models.
Ground-based spatially resolved near infrared spectroscopic observations of the
Venusian nightside have been obtained from Siding Spring Observatory at each
inferior conjunction since 2002. Observations have been made using the IRIS2
instrument on the Anglo-Australian Telescope and CASPIR on the 2.3m ANU telescope.
The model VSTAR (Bailey and Kedziora-Chudczer 2012) is used to simulate the
observed Venus spectra as seen through the Earth’s atmosphere and best fit water
vapour abundances are found for approximately 300 locations across the Venus
nightside disk. Recent improvements in ground-based near-infrared instruments
allow a substantial improvement in the spectral and spatial resolutions that can be
achieved, whilst recent updates to high temperature line lists have been critical to
improving the accuracy of spectroscopic modelling for the hot Venus atmosphere (Bailey
2009).
Prior to these studies, water vapour abundances have been derived by modelling the
spectral shape of the 1.18 μm window, in particular the gradient of the short wavelength wing
where water vapour has a strong influence (Meadows and Crisp, 1996; Bézard et al.,
2009,2011). Here we present best fit abundances and distributions determined by matching
water vapour absorption bands located at 1.174 μm, 1.178 μm and 1.182 μm. We compare
these results to those obtained by matching the short wing gradient of the 1.18 μm window.
Results confirm previous findings for a best fit water vapour abundance of 32ppmv in the
lower atmosphere and are consistent with no spatial variation. The 1.18 μm window has a
peak sensitivity at 16 km altitude, however we also outline a method by which it is
possible to obtain water vapour abundances from the near surface environment (0 – 4
km).
D.A. Allen and J.W. Crawford, Cloud structure on the dark side of Venus, Nature, Lond.
307 (1984), pp. 222–224.
J.Bailey, A comparison of water vapor line parameters for modeling the Venus deep
atmosphere, Icarus, 201 (2009), pp. 444-453.
J. Bailey and L. Kedziora-Chudczer, 2012, Modelling the spectra of planets, brown
dwarfs and stars using VSTAR, Mon. Not. R. Astr. Soc., 419, 1913-1929
B. Bézard, C. C. C. Tsang, R. W. Carlson, G. Piccioni, E. Marcq, and P. Drossart, Water
vapor abundance near the surface of Venus from Venus Express/VIRTIS observations, J.
Geophys. Res., 114, (2009) E00B39.
B. Bézard, A. Fedorova, J.-L. Bertaux, A. Rodin and O. Korablev, The 1.10 – and 1.18-
μm nightside windows of Venus observed by SPICAV-IR aboard Venus Express, Icarus, 216
(2011) 173-183.
V.S. Meadows, and D. Crisp, Ground-based near-infrared observations of the Venus
nightside: The thermal structure and water abundance near the surface, J. Geophys. Res.,
101(E2), (1996) pp. 4595–4622.
SC acknowledges support from the Portuguese Foundation for Science and Technology
through projects PTDC/CTE-AST/110702/2009 and PEst-OE/FIS/UI2751/2011. |
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