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Mapping zonal winds at Venus's cloud tops from ground-based Doppler velocimetry

P. Machado, D. Luz, T. Widemann, E. Lellouch, O. Witasse

Abstract
The most significant aspect of the general circulation of the atmosphere of Venus is its retrograde super-rotation. A complete characterization of this dynamical phenomenon is crucial for understanding its driving mechanisms. Here we report on ground-based Doppler velocimetry measurements of the zonal winds, based on high resolution spectra from the UV-Visual Echelle Spectrograph(UVES) instrument at ESO's Very Large Telescope. Under the assumption of predominantly zonal flow, this method allows the simultaneous direct measurement of the zonal velocity across a range of latitudes and local times in the day side. The technique, based on long slit spectroscopy combined with the high spatial resolution provided by the VLT, has provided the first ground-based characterization of the latitudinal profile of zonal wind in the atmosphere of Venus, the first zonal wind field map in the visible, as well as new constraints on wind variations with local time. We measured mean zonal wind amplitudes between 106 ± 21 and 127 ± 14 m/s at latitudes between 18°N and 34°S, with the zonal wind being approximately uniform in 2.6°-wide latitude bands(0.3 arcsec at disk center). The zonal wind profile retrieved is consistent with previous spacecraft measurements based on cloud tracking, but with non-negligible variability in local time(longitude) and in latitude. Near 50° the presence of moderate jets is apparent in both hemispheres, with the southern jet being stronger by ˜10 m/s. Small scale wind variations with local time are also present at low and mid-latitudes.

Keywords
Venus: Atmosphere - Atmospheres: Dynamics - Spectroscopy248

Icarus
Volume 221, Number 1, Page 248
2012 July

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Instituto de AstrofĆ­sica e CiĆŖncias do EspaƧo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa FundaĆ§Ć£o para a CiĆŖncia e a Tecnologia
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