Venus’ Cloud-Tracked Winds Using Ground- and Space-Based Observations with TNG/NICS and VEx/VIRTIS

Abstract

Characterizing the wind speeds of Venus and their variability at multiple vertical levels is essential for a better understanding of the atmospheric superrotation, constraining the role of large-scale planetary waves in the maintenance of this superrotation, and in studying how the wind field affects clouds’ distribution. Here, we present cloud-tracked wind results of the Venus nightside, obtained with unprecedented quality using ground-based observations during July 2012 with the near-infrared camera and spectrograph (NICS) of the Telescopio Nazionale Galileo (TNG) in La Palma. These observations were performed during 3 consecutive days for periods of 2.5 h starting just before dawn, sensing the nightside lower clouds of Venus close to 48 km of altitude with images taken at continuum K filter at 2.28 μm. Our observations cover a period of time when ESA’s Venus Express was not able to observe these deeper clouds of Venus due to a failure in the infrared channel of its imaging spectrometer, VIRTIS-M, and the dates were chosen to coordinate these ground-based observations with Venus Express’ observations of the dayside cloud tops (at about 70 km) with images at 380 nm acquired with the imaging spectrometer VIRTIS-M. Thanks to the quality and spatial resolution of TNG/NICS images and the use of an accurate technique of template matching to perform cloud tracking, we present the most detailed and complete profile of wind speeds ever performed using ground-based observations of Venus. The vertical shear of the wind was also obtained for the first time, obtained by the combination of ground-based and space-based observations, during the Venus Express mission since the year 2008, when the infrared channel of VIRTIS-M stopped working. Our observations exhibit day-to-day changes in the nightside lower clouds, the probable manifestation of the cloud discontinuity, no relevant variations in the zonal winds, and an accurate characterization of their decay towards the poles, along with the meridional circulation. Finally, we also present the latitudinal profiles of zonal winds, meridional winds, and vertical shear of the zonal wind between the upper clouds’ top and lower clouds, confirming previous findings by Venus Express.