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H. B. Hammel (MIT), K. A. Rages (SPRI, NASA Ames), G. W. Lockwood (Lowell)
HST imaging of Uranus in 1994 and 1997 revealed discrete cloud features suitable for wind tracking. In our 1997 data, we found wind speeds of 20.8 and 26.0 m/s at latitudes +23.5 and +25.6, respectively. Karkoschka (1998, Science 280, 570) detected features several days earlier in other HST imaging, finding velocities of 20.4 and 20.3 m/s at latitudes +27.2 and +27.5, suggesting a roughly constant velocity over 4 degrees of latitude (there is a hint in the Voyager data of similar structure from latitudes -35 to -38). The 1994 HST data yielded wind speeds that did not appear to match those seen by Voyager at similar latitudes (Hammel 1997, BAAS 29, 994). However, without a span of at least one rotation, the derived periods were highly uncertain. We fit all the data with the qualitative profile of Allison et al. (1991, in "Uranus," U. Ariz. Press, p. 253). The critical datum in the fits was the velocity of Karkoschka's discrete feature F at latitude +17, which was indeterminant from his observations (three possible values; see Karkoschka 1998). The fit with F2 (-27.1 m/s) was, at latitudes south of -20, virtually indistinguishable from the fit to Voyager data alone. In the northern hemisphere, the F2 fit passed through our 1997 points, but predicted faster winds at latitude +27 than those reported by Karkoschka (1998).
The author(s) of this abstract have provided an email address for comments about the abstract: hbh@alum.mit.edu