The two Titan stellar occultations of 14 November 2003
Publication date: 18 Nov 2006
Authors: Sicardy, B. et al.
Journal: Journal of Geophysical Research
Copyright: American Geophysical UnionWe report the observation of two stellar occultations by Titan on 14 November 2003, using stations in the Indian Ocean, southern Africa, Spain, and northern and southern Americas. These occultations probed altitudes between~550 and 250 km (~1 to 250 microbar) in Titan's upper stratosphere. The light curves reveal a sharp inversion layer near 515 ± 6 km altitude (1.5 microbar pressure level), where the temperature increases by 15 K in only 6 km. This layer is close to an inversion layer observed fourteen months later by the Huygens HASI instrument during the entry of the probe in Titan's atmosphere on 14 January 2005 [Fulchignoni et al., 2005]. Central flashes observed during the first occultation provide constraints on the zonal wind regime at 250 km, with a strong northern jet (~200 m s-1) around the latitude 55°N, wind velocities of ~150 m s-1 near the equator, and progressively weaker winds as more southern latitudes are probed. The haze distribution around Titan's limb at 250 km altitude is close to that predicted by the Global Circulation Model of Rannou et al. (2004) in the southern hemisphere, but a clearing north of 40°N is necessary to explain our data. This contrasts with Rannou et al.'s (2004) model, which predicts a very thick polar hood over Titan's northern polar regions. Simultaneous observations of the flashes at various wavelengths provide a dependence of tau ~ lambda-q , with q = 1.8 ± 0.5 between 0.51 and 2.2 micron for the tangential optical depth of the hazes at 250 km altitude.