Waves

Up until the end of the 1990s no wave structures had ever been observed in the Uranian atmosphere. However, near-IR Keck observations in 2003 (Hammel et al.,

Figure 5.38. Three HST/WFPC-2 images of Uranus, recorded in 1994 in a methane absorption band, revealing the motion of a pair of bright clouds in the planet's southern hemisphere, and a high-altitude haze that forms a "cap" above the planet's South Pole. The two high-altitude clouds are 4,300 and 3,100 km across, respectively. Three hours have elapsed between the first two images, and five hours have elapsed between the second pair of observations. Courtesy of NASA.

Figure 5.38. Three HST/WFPC-2 images of Uranus, recorded in 1994 in a methane absorption band, revealing the motion of a pair of bright clouds in the planet's southern hemisphere, and a high-altitude haze that forms a "cap" above the planet's South Pole. The two high-altitude clouds are 4,300 and 3,100 km across, respectively. Three hours have elapsed between the first two images, and five hours have elapsed between the second pair of observations. Courtesy of NASA.

2005a) found a subtle wave feature at the equator, with diffuse patches appearing every 30° in longitude, which is suggestive of an equatorially trapped Kelvin wave. Furthermore, in 2005, Keck observations of a very bright cloud at 30°N (Sromovsky et al., 2007) found that it oscillated its position in both latitude and longitude. The oscillation was modeled as being due to a slow-period Rossby wave combined with a shorter period inertial oscillation. Hence, it would seem that wave processes are likely to be as prevalent in Uranus' atmosphere as in the atmospheres of all the other giant planets, but have not been possible to observe until recently, when bright, trackable features have become observable.

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