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G. L. Bjoraker (NASA/GSFC), G. S. Orton (JPL), A. D. Collard (UK Meteorological Office), L. A. Sromovsky (U. of Wisconsin)
The CSHELL spectrometer at NASA's Infrared Telescope Facility was used in August and December 1996 to observe Jupiter at 5.18 microns. This wavelength sounds the 4-8 bar region in Jupiter's deep troposphere. The continuum level depends on the total cloud opacity above the 8-bar level, as is true of other parts of Jupiter's 5-micron window. The importance of this spectral region is due to a hot-band transition of CH4. The strength of this absorption feature is sensitive to the abundance of H2O vapor, the temperature of the line formation region, and the optical thickness of clouds in the 5 to 6-bar region. Radiative transfer models indicate that this CH4 feature should be strong in dry, clear regions such as the Galileo Probe Entry Site. The CH4 feature is predicted to be weak or absent in areas of Jupiter with saturated H2O vapor, thick H2O ice clouds, or both. Preliminary analysis of CSHELL data shows this line to be present in high-flux regions known from imaging studies as 5-micron hot spots. This allows us to extend the Galileo Probe in situ measurements of strongly subsaturated H2O to other regions. Further analysis and substantial spatial averaging will be required to determine whether low or intermediate flux regions exhibit this CH4 feature, implying subsaturated H2O, or whether the feature is absent, which would provide spectroscopic evidence for Jupiter's elusive water clouds.
The author(s) of this abstract have provided an email address for comments about the abstract: Gordon.Bjoraker@gsfc.nasa.gov