Winds From the Visible (513 nm) Images Obtained by the Venus Monitoring Camera Onboard Venus Express. Issue 4 (30th March 2022) - Khatuntsev, I. V.
Abstract: We present more than 250, 000 wind vectors derived from the visible (513 nm) images captured by the Venus Monitoring Camera (VMC) onboard ESA's Venus Express orbiter in the Southern hemisphere from 01 July 2007 to 29 January 2013. From comparison to the wind velocity derived from tracking of the descent probes, these measurements correspond to 60 ± 3 km altitude, being between two levels 70 ± 2 km and 55 ± 2 km, probed by VMC in ultraviolet (UV) (365 nm) and NIR (965 nm) channels, respectively. The mean zonal wind suggests retrograde circulation with mean zonal wind speed decreasing from 76.5 to 61.5 m/s at 30°–65°S. In low latitudes, 10–20°S, it increased to 82 m/s over the course of the mission. The mean zonal flow depends on local solar time and latitude and is affected by the large‐scale topography. The meridional winds indicated equatorward flow of up to 7 m/s in the middle and low cloud opposite to that derived from simultaneous UV observations at the cloud top. Plain Language Summary: Dynamics of the Venus atmosphere is dominated by a strong zonal retrograde circulation called "superrotation." The physical mechanisms maintaining this unique regime are poorly understood due to insufficient observational data. For about eight years, the Venus Monitoring Camera onboard ESA's Venus Express orbiter monitored motions of the cloud features in three spectral ranges: ultraviolet (UV) (365 nm), visible (513 nm), and near‐infrared (915 nm). These wavelengths probed different altitudes: 70 ± 2 km, 60 ± 3 km, and 55 ± 2 km correspondingly, thus providing wind field tomography. In this paper, we present more than 250, 000 wind vectors derived from the visible images. The results suggest decrease of the retrograde mean zonal wind speed from 76.5 to 61.5 m/s at 30°–65°S, and its increase up to 82 m/s at 10–20°S and show pronounced variations with local solar time, latitude, and surface topography. Interestingly, the meridional winds indicate equatorward flow of up to 7 m/s in the deep cloud opposite to that previously derived from UV images at the cloud top. Key Points: More than 250, 000 wind vectors at 57–63 km altitude were derived from the images taken by the Venus Monitoring Camera /Venus Express visible (513 nm) channel Mean zonal wind speed accelerated by ∼18.5 m/s at 30 ± 5°S over 8 Venusian years Zonal wind speed decreased from 85 m/s at the equator to 35 m/s at 80°S, meridional wind of up to 7 m/s velocity is directed equatorward