DPS 2001 meeting, November 2001
Session 22. Outer Planet Atmospheres II: Chemistry and Thermal Structure
Oral, Chairs: K. Rages, J. Moses, Wednesday, November 28, 2001, 3:00-4:30pm, Regency E

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[22.03] Cloud Structure on Uranus in 2001

H. B. Hammel (SSI), K. A. Rages (SPRI/Ames), G. W. Lockwood (Lowell), M. Marley (Ames)

HST images of Uranus were obtained in eight orbits in July 2001, with similar filters and temporal sampling as were used in June 2000. Discrete clouds are present at a variety of latitudes. We will report zonal velocities for those features with adequate coverage. The 619-nm (methane band) images, when compared with earlier 619-nm images taken by HST, reveal distinct changes in the brightness of the circumpolar region. In 1997, the region southward of -72 degrees grew steadily brighter toward the pole. In 2000, there was a brightness peak near -72 degrees; the polar latitudes were significantly darkened south of -75 degrees. The polar region appears to have brightened slightly in 2001; further analysis should distinguish between intrinsic variability of the aerosols or apparent variability due to changes in viewing geometry. The region between -50 and -65 degrees has also darkened since 1997 rendering the polar "collar" from -45 to -50 degrees more visible. In contrast, the regions from -30 to +10 degrees brightened uniformly since 1997. Latitudes from -10 to +10 degrees are still dominated by a bright fuzzy band, which appears slightly asymmetric with respect to the equator (shifted northward by about 1 degree). We also obtained infrared spectroscopy with SpeX at the IRTF in August 2001. Those data will be compared with similar observations obtained last year with the same instrument.

This work is supported in part by NASA Grant NAG5-10451 and STScI Grant GO-8680.05-A.

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