Wind circulation regimes at venus' cloud tops: Ground-based doppler velocimetry using CFHT/ESPaDOnS and comparison with simultaneous cloud tracking measurements using VEx/VIRTIS in February 2011

We present new results based on ground-based Doppler spectroscopic measurements, obtained with the ESPaDOnS spectrograph at Canada-France-Hawaii telescope (CFHT) and simultaneous observations of velocity fields, obtained from space by the VIRTIS-M instrument on board the Venus Express spacecraft. These measurements are based on high-resolution spectra of Fraunhofer lines in the visible to NIR range (0.37-1.05μm) acquired on February 19-21, 2011 at a resolution of about 80,000, measuring Venus' winds at 70km, using incoming solar radiation scattered by cloud top particles in the observer's direction (Widemann, T., et al., [2007]. Planet. Space Sci. 55, 1741-1756; Widemann, T., et al., [2008]. Planet. Space Sci. 56, 1320-1334). The zonal wind field has been characterized by latitudinal bands, at a phase angle Φ=(68.7±0.3)°, between +10°N and 60°S, by steps of 10°, and from [ϕ-ϕE]=-50° to sub-Earth longitude ϕE=0°, by steps of 12°. From space, VIRTIS-M UV (0.38μm) imaging exposures on the dayside were acquired simultaneously in orbit 1786, providing the first simultaneous cloud-tracking measurements with Doppler velocimetry. From the ground, we measured a zonal mean background velocity of v[U+203E]z=(117.3±18.0)ms-1 on February 19, andv[U+203E]z=(117.5±14.5)ms-1 on February 21. We detect an unambiguous poleward meridional flow on the morning dayside hemisphere of (18.8±12.3)ms-1 on February 19/21. Latitudinal variations of the zonal and meridional winds are further compared with the simultaneous VIRTIS data. We discuss temporal variability as well as its statistical significance. © 2014 Elsevier Inc.