TY - JOUR
T1 - Global circulation as the main source of cloud activity on Titan
AU - Rodriguez, Sébastien
AU - Le Mouélic, Stéphane
AU - Rannou, Pascal
AU - Tobie, Gabriel
AU - Baines, Kevin H.
AU - Barnes, Jason W.
AU - Griffith, Caitlin A.
AU - Hirtzig, Mathieu
AU - Pitman, Karly M.
AU - Sotin, Christophe
AU - Brown, Robert H.
AU - Buratti, Bonnie J.
AU - Clark, Roger N.
AU - Nicholson, Phil D.
N1 - Funding Information:
Acknowledgements We thank M. E. Brown for discussions that allowed us greatly to improve the quality of this study. This work was performed partly at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration. K.M.P. and J.W.B. are supported by the NASA Postdoctoral Program, administered by Oak Ridge Associated Universities. Calibrated VIMS data appear courtesy of the VIMS team. We thank the CNRS, CEA and CNES French agencies, as well as the Universities of Paris Diderot and Nantes for their financial support.
PY - 2009/6/4
Y1 - 2009/6/4
N2 - Clouds on Titan result from the condensation of methane and ethane and, as on other planets, are primarily structured by circulation of the atmosphere. At present, cloud activity mainly occurs in the southern (summer) hemisphere, arising near the pole and at mid-latitudes from cumulus updrafts triggered by surface heating and/or local methane sources, and at the north (winter) pole, resulting from the subsidence and condensation of ethane-rich air into the colder troposphere. General circulation models predict that this distribution should change with the seasons on a 15-year timescale, and that clouds should develop under certain circumstances at temperate latitudes (40°) in the winter hemisphere. The models, however, have hitherto been poorly constrained and their long-term predictions have not yet been observationally verified. Here we report that the global spatial cloud coverage on Titan is in general agreement with the models, confirming that cloud activity is mainly controlled by the global circulation. The non-detection of clouds at latitude 40°N and the persistence of the southern clouds while the southern summer is ending are, however, both contrary to predictions. This suggests that Titans equator-to-pole thermal contrast is overestimated in the models and that its atmosphere responds to the seasonal forcing with a greater inertia than expected.
AB - Clouds on Titan result from the condensation of methane and ethane and, as on other planets, are primarily structured by circulation of the atmosphere. At present, cloud activity mainly occurs in the southern (summer) hemisphere, arising near the pole and at mid-latitudes from cumulus updrafts triggered by surface heating and/or local methane sources, and at the north (winter) pole, resulting from the subsidence and condensation of ethane-rich air into the colder troposphere. General circulation models predict that this distribution should change with the seasons on a 15-year timescale, and that clouds should develop under certain circumstances at temperate latitudes (40°) in the winter hemisphere. The models, however, have hitherto been poorly constrained and their long-term predictions have not yet been observationally verified. Here we report that the global spatial cloud coverage on Titan is in general agreement with the models, confirming that cloud activity is mainly controlled by the global circulation. The non-detection of clouds at latitude 40°N and the persistence of the southern clouds while the southern summer is ending are, however, both contrary to predictions. This suggests that Titans equator-to-pole thermal contrast is overestimated in the models and that its atmosphere responds to the seasonal forcing with a greater inertia than expected.
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U2 - 10.1038/nature08014
DO - 10.1038/nature08014
M3 - Article
C2 - 19494910
AN - SCOPUS:66749107359
SN - 0028-0836
VL - 459
SP - 678
EP - 682
JO - Nature
JF - Nature
IS - 7247
ER -