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 (0.37–1.05 μm) acquired on February 19–21, 2011 at a resolution of about 80,000, measuring Venus’ winds at 70 km, 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 - ϕ E ] = - 50 ° to sub-Earth longitude ϕ E = 0 ° , by steps of 12°. From space, VIRTIS-M UV (0.38 μm) 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 ‾ z = ( 117.3 ± 18.0 ) m s - 1 on February 19, and v ‾ z = ( 117.5 ± 14.5 ) m s - 1 on February 21. We detect an unambiguous poleward meridional flow on the morning dayside hemisphere of (18.8 ± 12.3) m s−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.