Atmospheric gravity waves in Venus dayside clouds from VIRTIS-M images

We perform a survey of the Visible and Infrared Thermal Imaging Spectrometer-Mapper (VIRTIS-M) images onboard the Venus Express space mission, at four narrow wavelength bands that target different altitude regions on the cloud deck of Venus' atmosphere (280–320, 365–400, 580–600, 900–920 nm). Our goal was to detect and characterize atmospheric gravity waves, using several processing techniques based on high-pass filtering to enhance features in low-contrast images. The period of our selected dataset was between August 2007–October 2008 on the dayside hemisphere, identical to a previous study of waves located on the nightside lower cloud, so that a temporally overlapped comparison could be established, although over different longitudinal locations. We retrieved the morphological properties of these waves including horizontal wavelength and packet width along with several orientations of the identified waves. We retrieved properties for 69 wave packets across all analysed wavelength ranges, and dynamical parameters for 16 wave packets. Waves observed across the four wavelength ranges examined here have similar properties, with horizontal wavelengths of a few hundred kilometres and full length of wave-trains going up to 1000 km. Although these wave properties do not seem to depend on latitude, we notice an increase in the values of several of these parameters close to the evening terminator. Considering our results and a comparison with previous studies of stationary features interpreted as gravity waves, we argue that forcing from topography is not the main cause of the wave packets observed here, whose properties are better supported by a convective generation scenario. The retrieved properties show a consistent agreement between waves on the upper and lower cloud, suggesting a similar forcing mechanism based on convection from a neutral stability layer between the lower and middle-upper cloud. Despite the similar properties, we find no evidence of any correlation between wave packets propagating in the lower cloud and upper cloud, based on their shape and relative position.