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P. G. Steffes, T.R. Hanley (Georgia Inst. of Tech.), D.R. DeBoer (SETI Institute)
Next to ammonia, no polar molecule has been studied as extensively for its microwave and millimeter-wave properties as has water vapor. Surprisingly however, only very limited laboratory studies of the centimeter-wave properties of water vapor under conditions characteristic of the outer planets have been conducted. This is likewise surprising given the current interest in using passive microwave radiometry for measurement of the deep atmospheric abundance of water vapor at Jupiter. (See, e.g., Janssen et al. ICARUS 2004 or dePater et al. ICARUS 2004).
A program of laboratory measurements is now being initiated to measure the opacity of water vapor in a hydrogen/helium atmosphere in the 1.3 to 20 cm wavelength range. Measurements will be conducted at pressures from 5 to 16 Bars and at temperatures corresponding to those pressures in the Jovian atmosphere (approximately 290-400 K). As a proof of concept, a preliminary measurement of the centimeter-wave (1.3-20 cm) opacity of a mixture consisting of 2% water vapor, 84.7% hydrogen, and 13.3% helium was conducted at a pressure of 6.9 Bars and a temperature of 373 K. The results placed upper limits on the cm-wave opacity from water vapor which were consistent with the model from Goodman (Ph.D. thesis, 1969) but were inconsistent with the model described in DeBoer (Ph.D. thesis, 1995). Corrections to errors in the text of the DeBoer (1995) model have now been identified (dePater et al. ICARUS 2004), and the model is shown to be consistent with the preliminary laboratory results.
This work is supported by the NASA Planetary Atmospheres Program under grant NAG5-12122.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.