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| Titel |
New measurements of Venus winds with ground-based Doppler velocimetry at CFHT |
| VerfasserIn |
P. Machado, T. Widemann, D. Luz, J. Peralta, D. L. Berry |
| 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 |
250068072
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| Zusammenfassung |
| Since Venus Express spacecraft operations started in 2006, an ongoing effort has been made
to coordinate its operations with observations from the ground using various techniques and
spectral domains (Lellouch and Witasse, 2008). We present an analysis of Venus Doppler
winds at cloud tops based on observations made at the Canada France Hawaii 3.6-m telescope
(CFHT) with the ESPaDOnS visible spectrograph. These observations consisted of
high-resolution spectra of Fraunhofer lines in the visible range (0.37–1.05 μm) to measure
the winds at cloud tops using the Doppler shift of solar radiation scattered by cloud top
particles in the observer’s direction (Widemann et al., 2007, 2008). The observations were
made during 19-20 February 2011 and were coordinated with Visual Monitoring
Camera (VMC) observations by Venus Express. The complete optical spectrum was
collected over 40 spectral orders at each point with 2-5 seconds exposures, at a
resolution of about 80000. The observations included various points of the dayside
hemisphere at a phase angle of 67º, between +10Ë and -60Ë latitude, in steps of 10Ë ,
and from +70Ë to -12Ë longitude relative to sub-Earth meridian in steps of 12Ë
.
The Doppler shift measured in scattered solar light on Venus dayside results from two
instantaneous motions: (1) a motion between the Sun and Venus upper cloud particles; (2) a
motion between the observer and Venus clouds. The measured Doppler shift, which results
from these two terms combined, varies with the planetocentric longitude and latitude and is
minimum at meridian ΦN = ΦSun – ΦEarth where the two components subtract to each
other for a pure zonal regime. Due to the need for maintaining a stable velocity reference
during the course of acquisition using high resolution spectroscopy, we measure
relative Doppler shifts to ΦN. The main purpose of our work is to provide variable
wind measurements with respect to the background atmosphere, complementary to
simultaneous measurements made with the VMC camera onboard the Venus Express. We
will present first results from this work, comparing with previous results by the
CFHT/ESPaDOnS and VLT-UVES spectrographs (Machado et al., 2012), with Galileo fly-by
measurements and with VEx nominal mission observations (Peralta et al., 2007, Luz et al.,
2011).
Acknowledgements: The authors acknowledge support from FCT through projects
PTDC/CTE-AST/110702/2009 and PEst-OE/FIS/UI2751/2011. PM and TW also
acknowledge support from the Observatoire de Paris.
Lellouch, E., and Witasse, O., A coordinated campaign of Venus ground-based
observations and Venus Express measurements, Planetary and Space Science 56 (2008)
1317–1319.
Luz, D., et al., Venus’s polar vortex reveals precessing circulation, Science 332 (2011)
577-580.
Machado, P., Luz, D. Widemann, T., Lellouch, E., Witasse, O, Characterizing the
atmospheric dynamics of Venus from ground-based Doppler velocimetry, Icarus,
submitted.
Peralta J., R. Hueso, A. Sánchez-Lavega, A reanalysis of Venus winds at two cloud levels
from Galileo SSI images, Icarus 190 (2007) 469–477.
Widemann, T., Lellouch, E., Donati, J.-F., 2008, Venus Doppler winds at Cloud Tops
Observed with ESPaDOnS at CFHT, Planetary and Space Science, 56, 1320-1334. |
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