Global mean cloud coverage on Venus in the near-infrared

We present a map of the global mean lower cloud coverage of Venus. This map is the average of 35 nights of 2.26 μm night side observations taken at NASA's Infrared Telescope Facility on Mauna Kea, over the years spanning 2001-2007. The atmosphere of Venus is a very dynamic system, and the lower clouds are constantly changing [Crisp, D., Allen, D.A., Grinspoon, D.H., Pollack, J.B., 1991a. The dark side of Venus: near-infrared images and spectra from the Anglo-Australian Observatory. Science, 253, 1263-1266]. By studying average cloud coverage, the daily variations are suppressed in order to see the underlying persistent cloud pattern. We find a relatively thick but highly variable equatorial band of clouds (±20° in latitude) and more quiescent mid-latitude clouds that are less opaque on average, with persistent cloudiness near the poles. We show that there is enough variation between our daily observations or between observations taken in different months that they cannot be considered individually representative of the global mean. We also compare the cloud coverage map to the topography of Venus and find no definitive correlations with high altitude features.