Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p31c1549g&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P31C-1549
Physics
[3337] Atmospheric Processes / Global Climate Models, [5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [6281] Planetary Sciences: Solar System Objects / Titan
Scientific paper
Saturn’s moon Titan has a methane cycle akin to Earth’s water cycle, with methane evaporating from lakes, condensing in clouds, and precipitating as rain. Titan has been observed in detail for a decade, from its southern summer solstice through vernal equinox. In this time, key observations include methane clouds in southern middle and high latitudes, dry and dune-covered low latitudes, and lakes in polar regions, preferentially in the north. No model has fully explained these features. Here we use a three-dimensional general circulation model (GCM) that includes a methane surface reservoir to show that the atmospheric circulation and its annual cycle can account for the observed methane cloud and lake distributions. Deep convective clouds form in the summer hemisphere—at the pole and in mid-latitudes—in rising branches of the mean meridional circulation. Lakes form in polar regions because methane transported toward the summer pole is cold-trapped there; more lakes form in the north because northern summer is colder than southern summer owing to Saturn’s orbital eccentricity. In southern hemisphere late summer, south polar lakes in the GCM experience a net evaporative methane loss (the difference between evaporation and precipitation rates) of ˜0.5 m/yr (1 yr referring to 1 Earth year). This is of the same magnitude as the drop in south polar lake levels observed between 2005 and 2009 [1]. The GCM predicts changes that will soon be observable: prominent cloud formation will begin in the northern middle and high latitudes within ~3 years, and lake levels near the north pole will rise over the next ~15 years. [1] Hayes, A. et al. Transient surface liquid in Titan’s polar regions from Cassini. Icarus (in press).
Brown Michael E.
Graves Sharon S.
Schaller Emily L.
Schneider Tapio
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