37th DPS Meeting, 4-9 September 2005
Session 22 Outer Planets II
Oral, Tuesday, September 6, 2005, 11:00am-12:30pm, Law LG19

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[22.08] Imaging the Troposphere of Uranus at Millimeter and Centimeter Wavelengths

M. D. Hofstadter (JPL), B. J. Butler (NRAO), M. A. Gurwell (SAO)

We recently imaged Uranus at five wavelengths from 0.7 to 20 cm, using the Very Large Array interferometer. These continuum measurements of thermal emission probe the temperature and composition of the atmosphere at pressures between 0.5 and 50 bars. Our measurements extend the time and frequency coverage of an ongoing effort to study atmospheric circulation and variability as Uranus passes through its 2007 equinox. Preliminary results are:

1) At all wavelengths and in both hemispheres, latitudes poleward of 45 degrees are much brighter than lower latitudes, typically by tens of Kelvin. These regions are probably depleted in absorbers at the altitudes we probe.

2) The contrast between bright poles and dim equator may be smallest at 20 cm. (Analysis of these data, which have the poorest spatial resolution, is not yet complete).

3) At 0.7 and 1.3 cm (wavelengths most sensitive to ammonia vapor), banding is evident at equatorial latitudes. This banding is not seen at wavelengths longer than 2 cm.

We will discuss the ramifications of these observations, including differences between the deep-seated polar features and the (vertically restricted?) equatorial banding, a comparison of the polar vortices on Jupiter and Saturn (Orton and Yanamandra-Fisher 2005, Science 307) and the features on Uranus, and we will explore if the top of the liquid water cloud (best seen in our 20 cm data) marks a transition to latitudinally more uniform conditions. We will also discuss why the temperature and composition fields seen by our wavelengths are hemispherically symmetric, while high altitude aerosols seen at near-IR wavelengths (Hammel et al. 2005, Icarus 175) are hemispherically asymmetric.

This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. We acknowledge the assistance of the NRAO, operated by Associated Universities, Inc., under contract with the NSF.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.