Venus Doppler winds at cloud tops observed with ESPaDOnS at CFHT

We present new wind measurements in Venus' lower mesosphere from visible spectroscopy during the 2007 worldwide coordinated ground campaign in support of ESA's Venus Express mission. These observations consisted of high-resolution spectra of Fraunhofer lines in the entire visible range (0.37-1.05 μm) to measure the winds near 68 km using the Doppler shift of solar radiation scattered by clouds toward the observer's direction. The observations included various points of the dayside hemisphere at a phase angle of ∼109°. We took advantage of two symmetrical elongations in July and September 2007 at Canada-France-Hawaii's 3.6-m telescope. Kinematical fits to the Doppler winds provide a mean equatorial velocity of (104±10) m s−1 for the zonal retrograde flow. This velocity agrees quite well with the mean value obtained by tracking the UV markings from several spacecraft.