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| Titel |
Investigation of winds in Venus mesosphere by digital method using UV images from VMC aboard Venus Express. |
| VerfasserIn |
Marina Patsaeva, Igor Khatuntsev, Nikolai Ignatiev |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076748
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| Zusammenfassung |
| Investigation of winds at the top cloud layer is important for understanding the
global circulation of the Venus atmosphere. The Venus Monitoring Camera (VMC)
aboard Venus Express has acquired a huge number of UV (365 nm) images. UV
images of top cloud layer are customary to obtain the wind velocity due to their
high contrast. Visual estimation of wind velocities is a labor intensive procedure.
Authors have developed a digital method to estimate velocities of shifts of cloud
details.
The method is based on analysis of correlations between two UV images acquired at
different moments. The method takes into account the change of a correlation function due to
latitudinal peculiarities of cloud morphology and eliminates image regions which are far from
the sub-spacecraft point. The digital method provides with good vector coverage
of the Venus day side (9-16 local time) from the equator to high latitudes. The
best agreement between the digital and visual methods is observed at low latitudes
(below 35S). The discrepancy at higher latitudes is related to complicated cloud
morphology, namely domination of streaks, which increases errors in the zonal wind
speed. The method is productive for long-scale circulation at the top cloud layer.
Sizes of regions for correlation were chosen empirically as a trade-off of sensitivity
against noise immunity and varies from 10x7.5 º to 20x10 º depending on grid
step.
580 orbits covering ten Venus years have been processed by using the digital
method. The database of shift vectors counts about 400000 records. The mean wind
speed at low latitudes is about 100 m/s. Wind vector fields were obtained for every
orbit. The zonal wind speed in the equatorial region exhibits short-period (about 4.8
days) and long-period variations (long-term trend). Vector field averaged by all
orbits show deviations of the main stream up to 5 degrees poleward in the early
afternoon (12.5-14.5h) at 45-55S. The mean absolute value of the wind speed increases
from 59.38 m/s at 10-12h to 76.46 m/s at 12.5-14.5h at the same latitude interval. |
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