I present an analysis of visible and near-infrared adaptive optics images and spectra of Titan taken over 43 nights between October 1997 and January 2003 with the AEOS 3.6-m, Palomar Hale 5-m, and W.M. Keck 10-m telescopes. These observations reveal a seasonally changing stratospheric haze layer, two distinct regions of condensate clouds in the southern hemisphere, the albedo of Titan's surface, and the zonal wind field of the stratosphere.
Transient convective CH4 clouds are identified near Titan's south pole, rising to 16±5 km above the surface. These clouds have been continuously present south of 70°S since at least December 2001, currently account for 0.5-1% of Titan's 2 μm flux, and appear to be gradually brightening or thickening as the insolation of the south polar region increases. Above the polar clouds, an extensive but optically thin (τ∼0.05 at 2μm ) cloud layer is noted near the tropopause south of 30°S. This cirrus-like structure has remained unchanged in extent and thickness since September 1999 despite seasonal changes in the underlying convective clouds and the overlying stratospheric haze. Aside from the convective CH4 clouds near the south pole, Titan's troposphere is free of aerosols with an upper limit of τ<0.01 on the 2 μm vertical optical depth in the 5-30 km altitude region.
The albedo of Titan's surface at 2.0 μm is derived from the radiative transfer analysis of spatially resolved spectra and images, and presented in the form of a ∼600 km resolution global surface albedo map. At this resolution, the 2.0 μm albedo ranges from 0.05 to 0.17, consistent with extensive exposure of clean water ice in some regions, while hydrocarbons and atmospheric sediments blanket others.
The zonal wind field of Titan's stratosphere near southern
summer solstice is derived from adaptive optics observations of
the occultation of a binary star on 20 December 2001.
Multiple refracted stellar images were detected on Titan's limb
during the each successive occultation, allowing the angular
deflection of the starlight at two altitudes over both hemispheres
to be measured with an uncertainty of ∼2 milliarcseconds.
The zonal wind field derived from this measurement of the shape of
Titan's limb exhibits strong but asymmetric high latitude jets,
with peak wind speeds of 230±20 m s-1 at 60°N
and 160±40 m s-1 at 40°S, and lower winds
of 110±40 m s-1 at the equator.
The direction of the wind is not constrained.
| Full Thesis (160 pages, PostScript 54Mb, PDF 4Mb) | ps | |
| Title, abstract, acknowledgements, table of contents | ps | |
| Ch 1. Introduction | ps | |
| Ch 2. Visible adaptive optics observations of Titan's atmosphere and surface | ps | |
| Ch 3. Spatially resolved spectroscopy of Titan | ps | |
| Ch 4. Titan's stratospheric winds | ps | |
| Ch 5. Direct detection of variable tropospheric clouds near Titan's south pole | ps | |
| Ch 6. Seasonal change in Titan's tropospheric clouds | ps | |
| Ch 7. A photometric search for clouds on Titan | ps | |
| Appendix. Thesis data | ps | |
| Bibliography | ps |