Monitoring atmospheric phenomena on Titan

Mathieu Hirtzig (1) , Athena Coustenis (1) , Eric Gendron (1) , Pierre Drossart (1) , Alberto Negrão (1, 2) , Michel Combes (1) , Olivier Lai (1, 3) , Pascal Rannou (2) , Sébastien Lebonnois (4) , David Luz (1)

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 SA - Service d'aéronomie
3 CFHT - Canada-France-Hawaii Telescope Corporation
4 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)

For the past 8 years (1998-2005), we have used adaptive optics imaging (with VLT/NACO and CFHT/PUEO) to explore Titan's atmosphere, which is currently scrutinized in situ by the Cassini-Huygens mission. In the course of our work, we have found variations, such as as seasonal and diurnal effects, as well as temporary features in the southern polar region. The north-south asymmetry is shown to have changed since 2000 in the near-IR and to be currently organized in a brighter northern than southern pole. We study this evolution here. With our data, we also have new significant statistical evidence of diurnal effects in Titan's stratosphere, with a brighter (as much as 19%) morning limb appearing in our images in many cases, when the phase effect is expected on the evening side. The southern bright feature is probably a time-limited seasonal and/or meteorological phenomenon, revolving around the south pole (confined in its motion within the 80$^{\circ}$S parallel) and located somewhere in the upper troposphere (18-40 km of altitude). Its behavior and possible nature are discussed here.

Mots clés: Titan; observation

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]

Mathieu Hirtzig, Athena Coustenis, Eric Gendron, Pierre Drossart, Alberto Negrão, et al.. Monitoring atmospheric phenomena on Titan. Astronomy and Astrophysics - A&A, 2006, 456 (2), pp.761-774. ⟨10.1051/0004-6361:20053381⟩. ⟨hal-00093994⟩