DPS 34th Meeting, October 2002
Session 13. Outer Planets: Atmospheric Dynamics, Clouds
Oral, Chair(s): G.S. Orton and K.A. Rages, Tuesday, October 8, 2002, 1:30-3:30pm, Room M

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[13.09] Seasonal Evolution of Uranus' South Polar Cap

K. A. Rages (SETI Inst.), H. B. Hammel (Space Sci. Inst.), G. W. Lockwood (Lowell Obs.), M. Marley (NASA Ames)

Hubble Space Telescope (HST) images of Uranus (spatial resolution ~3\deg of latitude) now cover a period of seven yearsi --equivalent to about one uranian month-- and the inclusion of Voyager data extends the period of spatially resolved coverage to almost the whole of southern hemisphere winter. During the HST era, the polar collar near 45\deg S has become more distinct in broadband near-IR filters, and a slightly darker ring near 75\deg S has become detectable at 791 nm. In addition to seasonal (~decades) variability, there is evidence for intrinsic changes of ~10% in the south polar cap on time scales of (terrestrial) months. We present the results of radiative transfer modeling to determine how the methane cloud optical depth and single scattering albedo at several latitudes have varied over the past seven years.

This work was funded through NASA Grants GO-08680.03-A and GO-08634.01-A, submitted to the Space Science Telescope Institute, which is operated by the Association of Universities for Research in Astronomy.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.