1. Laboratoire de Planétologie et Géodynamique, CNRS, UMR 6112, Université de Nantes, 2 rue de la Houssinière, 44000 Nantes, France
2. Laboratoire AIM, Université Paris 7, CNRS UMR-7158, CEA-Saclay/DSM/IRFU/SAp, 91191 Gif/Yvette, France
3. Groupe de Spectrométrie Moléculaire et Atmosphérique, CNRS UMR-6089, Université de Reims Champagne-Ardenne, 51687 Reims, France
4. LATMOS, CNRS UMR-7620, Université Versailles-St-Quentin, 91371 Verrières-le-Buisson, France
5. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109-8099, USA
6. NASA Ames Research Center M/S 244-30, Moffett Field, California 94035, USA
7. Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721-0092, USA
8. AOSS, PSL, University of Michigan, Ann Arbor, Michigan 48109, USA
9. USGS, Denver Federal Center, Denver, Colorado 80225, USA
10. Cornell University, Astronomy Department, Ithaca, New York 14853, USA

Correspondence to: Sébastien Rodriguez^1,2 Correspondence and requests for materials should be addressed to S.R. (Email: sebastien.rodriguez@cea.fr).

Clouds on Titan result from the condensation of methane and ethane and, as on other planets, are primarily structured by circulation of the atmosphere^{1, 2, 3, 4}. At present, cloud activity mainly occurs in the southern (summer) hemisphere, arising near the pole^{5, 6, 7, 8, 9, 10, 11, 12} and at mid-latitudes^{7, 8, 13, 14, 15} from cumulus updrafts triggered by surface heating and/or local methane sources, and at the north (winter) pole^{16, 17}, resulting from the subsidence and condensation of ethane-rich air into the colder troposphere. General circulation models^{1, 2, 3} 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 hemisphere². 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 Titan's 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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