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M. Hofstadter (JPL), T. Readhead (Caltech), S. Gulkis (JPL), R. Reeves (Univ. de Concepcion)
The Cosmic Background Imager (CBI) is an interferometer working in the 26 to 36 GHz range (0.8 to 1.2 cm). Located in the Chilean Andes at an altitude of 16,700 feet, it was designed for cosmological studies of the cosmic microwave background. We have used the CBI to make precise measurements of Jupiter's total flux at radio wavelengths. By tieing CBI measurements to those of the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, we have obtained absolute radiances with a 1-sigma uncertainty of +-1.3%. Relative temperatures within the above frequency range are accurate to +-0.6%.
Jupiter's spectrum at these wavelengths is dominated by the strong NH3 inversion band. The CBI data, sampling the wings of this absorption band, sound the atmosphere in the region of the assumed NH3 cloud, near 1 bar. Preliminary analysis indicates the globally averaged relative humidity of NH3 above its cloud base is in the 30 to 75% range. Uncertainty in our knowledge of the ammonia lineshape contributes as much to this spread as the uncertainty in the data. This result is in qualitative agreement with earlier work (for example, Klein and Gulkis 1978, Icarus 35; Fouchet et al. 2000, Icarus 143; de Pater et al. 2001, Icarus 149). At the meeting, we will present our analysis of CBI and WMAP data. These data provide some of the strongest constraints to date on the global behavior of ammonia in its cloud-forming region.
Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.