Monday, October 17, 2011

Predicting Rain on Titan

     Saturn’s largest moon, Titan, has an active weather cycle, with methane clouds and liquid methane rain. In September and October last year, a few distinctive clouds were detected by the Cassini spacecraft: arrow-shaped formations near the equator and sheared streaks at mid-southern latitudes.
    Mitchell et al. found similar features at similar latitudes in their three-dimensional model of the general circulation of Titan’s atmosphere. The calculations reveal that the features are not isolated occurrences but are instead shaped by large-scale atmospheric waves that are similar to those that account for intraseasonal variability in Earth’s tropics. 
   The model predicts several centimeters of precipitation over regions on scales exceeding 1000 km associated with the clouds. Such amounts could cause Titan’s low-latitude deserts to be shaped by seasonal fluvial erosion. Previous observations have shown sudden surface changes near Titan’s equator after the arrowshaped cloud outburst that was interpreted as signs of rainfall. Precipitation from the midsouthern latitude streaks has not been detected by observations, which suggests that the model overestimates mid-latitude precipitation during the current season.



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