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| Titel |
VEx/VIRTIS and TNG/NICS cloud tracked winds at Venus’ lower cloud level using nightside observations |
| VerfasserIn |
Pedro Machado, Javier Peralta, David Luz, Rúben Gonçalves |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125247
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| Publikation (Nr.) |
 EGU/EGU2016-4806.pdf |
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| Zusammenfassung |
| We present results based on observations carried out with the Near Infrared Camera and
Spectrograph (NICS) of the Telescopio Nazionale Galileo (TNG), in La Palma, on July 2012.
We observed for periods of 2.5 hours starting just before dawn, for three consecutive nights.
We acquired a set of images of the night side of Venus with the continuum K filter at 2.28
microns, which allows to monitor motions at the lower cloud level of the atmosphere of
Venus, close to 48 km altitude. Our objective has been to measure the horizontal wind
field in order to characterize the latitudinal zonal wind profile, to study variability,
to help constrain the effect of large scale planetary waves in the maintenance of
superrotation, and to map the cloud distribution. We will present first results of cloud
tracked winds from ground-based TNG observations and winds retrieved from
coordinated space-based VEx/VIRTIS observations. The cloud deck extends in altitude
from 45 to 70 km, and can be divided into three main regions, centered at 48, 54
and 60 km. The lowest of these is the lower cloud, where fundamental dynamical
exchanges that help maintain superrotation are thought to occur. The lower venusian
atmosphere is a strong source of thermal radiation, with the gaseaous CO2 component
allowing radiation to escape in windows at 1.74 and 2.28 μm. At these wavelengths
radiation originates below 35 km, and unit opacity is reached at the lower cloud level,
close to 48 km. Therefore, in these windows it is possible to observe the horizontal
cloud structure, with thicker clouds seen silhouetted against the bright thermal
background from the low atmosphere. Our objective is to provide direct absolute
wind measurements and a map of cloud distribution at the lower cloud level in
the Venus troposphere, in order to complement Venus Express (VEX) and other
ground-based observations of the cloud layer wind regime. By continuous monitoring of the
horizontal cloud structure at 2.28 μm (NICS Kcont filter), it is possible to determine
wind fields using the technique of cloud tracking. We acquired a series of short
exposures of the Venus disk. Cloud displacements in the night side of Venus were
computed taking advantage of a phase correlation semi-automated technique. The
Venus apparent diameter at observational dates was greater than 32” allowing a
high spatial precision. The 0.13” pixel scale of the the NICS narrow field camera
allowed to resolve ∼ 3-pixel displacements. The absolute spatial resolution on the
disk was ∼ 100 km/px at disk center, and the (0.8–1") seeing-limited resolution
was ∼ 400 km/px. By co-adding the best images and cross-correlating regions
of clouds the effective resolution was significantly better than the seeing-limited
resolution. In order to correct for scattered light from the (saturated) day side crescent
into the night side, a set of observations with the Brγ filter were performed. Cloud
features are invisible at this wavelength due to the high optical depth of the gaseous
CO2 component, and this technique allows for a good correction of scattered light. |
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