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| Titel |
VENUS EXPRESS: a four-year survey of the atmosphere of Venus |
| VerfasserIn |
Dmitriy Titov, Håkan Svedhem, Fredric W. Taylor |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042187
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| Zusammenfassung |
| Since April 2006 Venus Express has been performing a global survey of the remarkably
dense, cloudy, and dynamic atmosphere of our near neighbour. A consistent picture of the
climate on Venus is emerging on the basis of the new data, which enables us to provide an
overview of the global temperature structure, the composition and its variations, the cloud
morphology at various levels, the atmospheric dynamics and general circulation, and
near-infrared emissions from trace species such as oxygen in the mesosphere. Vertical
profiles of atmospheric temperature in the mesosphere and upper troposphere show strong
variability correlated with changes in the cloud top structure and many fine details indicating
dynamical processes. Temperature sounding also shows that the main cloud deck at
50-60 km is convectively unstable over large portion of the planet, in agreement
with the analysis of UV images. Imaging also reveals strong latitudinal variations
and significant temporal changes in the global cloud top morphology, which will
inevitably modulate the solar energy deposited in the atmosphere. The cloud top
altitude varies from ~72 km in the low and middle latitudes to ~64 km in the polar
region, marking vast polar depressions that form as a result of the Hadley-type
meridional circulation. Stellar and solar occultation measurements have revealed an
extended upper haze of submicron particles and provided information on its optical
properties. Solar occultation observations and deep atmosphere spectroscopy in several
spectral transparency windows have quantified the distribution of the major trace
gases H2O, SO2, CO, COS and their variations above and below the clouds, and so
provided important input and validation for models of chemical cycles and dynamical
transport. Cloud motion monitoring has characterised the mean state of the atmospheric
circulation as well as its variability. Low and middle latitudes show an almost constant
zonal wind speed of 100+/-20 m/s at the cloud tops and vertical wind shear of 2-3
m/s/km. Towards the pole, the wind speed drops quickly and the vertical shear
vanishes. The meridional poleward wind ranges from 0 to about 15 m/s and there is
some indication that it may change its direction at high latitudes. Comparison of
the thermal wind field derived from temperature sounding to the cloud tracked
winds confirms the approximate validity of cyclostrophic balance, at least in the
latitude range from 30 S to 70 S. Non-LTE infrared emissions in the lines of O2, NO,
CO2, OH originating near the mesopause at 95-105 km altitude were detected and
mapped on the night side. The data show that the airglow peak intensity occurs
close to the anti-solar point and its location depends on particular specie. These
observations result in significant improvement of thermospheric circulation models. |
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