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C. A. Griffith (Northern Arizona University), J. L. Hall (UC Berkeley), E. F. Young (Southwest Research Institute), J. Cook (Arizona State University), P. Rannou (Université de Paris)
We investigate Hubble Space Telescope images of three separate sources of particulates that vary temporally and spatially across Titan's disk. (1) North-south variations of Titan's albedo occur at visible wavelengths that result from seasonal changes in the number density of haze at Titan's stratopause (roughly 250 km altitude). The phase lag in these periodic variations match that of Titan's temperature field and support the hypothesis that the thermal profile reacts in concert with the wind field through the wind gradient equation. This coupling causes the thermal field to adjust to seasonal changes at a dynamical time scale of approximately 5 years, much longer than the radiative time scale. (2) Images at longer wavelengths (0.7-1 um) indicate the presence of particles near Titan's tropopause and lower stratosphere at high southern latitudes. The nature of these particles is unclear. Their absence at northern latitudes precludes a purely circulation origin. Their lack of measurable change from 1994 to 2000, precludes convective origins. (3) We detect one occurrence of a brightening at Titan's equator, unrelated to the stratosphere and the surface. Judging by its temporal nature and altitude of 20-40 km, this may an image of methane condensation clouds in Titan's atmosphere.
This research is supported by the NASA Planetary Astronomy Program and the Hubble Space Telescope Program.
The author(s) of this abstract have provided an email address for comments about the abstract: griffith@vela.phy.nau.edu