Discovery of lake-effect clouds on Titan.pdf

Discovery of Lake-effect clouds on Titan M.E. Brown 1 , E.L. Schaller 1 , H.G. Roe 2 , C. Chen 1,3 , J. Roberts 1 , R.H. Brown 4 , K.H. Baines 5 , R.N. Clark 6 Abstract: Images from instruments on Cassini as well as from telescopes on the ground reveal the presence of sporadic small-scale cloud activity in the cold late-winter north polar of Saturn’s large moon Titan. These clouds lie underneath the previously discovered uniform polar cloud attributed to a quiescent ethane cloud at ~40 km and appear confined to the same latitudes as those of the largest known hydrocarbon lakes at the north pole of Titan. The physical properties of these clouds suggest that they are due to methane convection and condensation. Such convection has not been predicted for the cold winter pole, but can be caused by a process in many ways analogous to terrestrial lake-effect clouds. The lakes on Titan are a key connection between the surface and the meteorological cycle. 1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 USA 2 Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001 USA 3 Westridge School, 324 Madeline Dr., Pasadena, CA 91105 USA 4 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 USA 5 Jet Propulsion Laboratory, Pasadena, CA 91109 USA 6 US Geological Survey, Mail Stop 964, Box 25046 Federal Center, Denver, CO 80225 USA 1. Introduction Tropospheric cloud cover on Titan is significantly more sparse and more variable than on the Earth, with typical surface coverage being less than 1%, but with large storms occasionally covering up to 10% of the surface [Griffith et al., 1998; Griffith et al., 2000; Schaller et al., 2006a]. The locations of the clouds appear to be controlled by solar insolation. During southern summer solstice, when the point of maximum insolation was the pole itself, clouds were a persistent pre