Global circulation as the main source of cloud activity on Titan

Research areas:
Year:
2009
Authors:
Journal:
NATURE
Volume:
459
Number:
7247
Pages:
678-682
Month:
JUN 4
ISSN:
0028-0836
Abstract:
Clouds on Titan result from the condensation of methane and ethane and,
as on other planets, are primarily structured by circulation of the
atmosphere(1-4). At present, cloud activity mainly occurs in the
southern (summer) hemisphere, arising near the pole(5-12) and at
mid-latitudes(7,8,13-15) 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(1-3) 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 (similar to 40 degrees) in
the winter hemisphere(2). 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 similar to 40 degrees 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.