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G. L. Bjoraker (NASA/GSFC), T. Hewagama (U. Md at GSFC), M. Roos-Serote (Lisbon Astronomical Observatory), G. S. Orton, R. W. Carlson (JPL)
The CSHELL spectrometer at NASA's Infrared Telescope Facility was used in December 1996 to observe Jupiter at nearly the same time as Galileo/NIMS observations of a hot spot in the North Equatorial Belt (NEB). CSHELL spectra of CH4 at 5.18 microns and NIMS spectra of H2O between 4.6 and 5.2 microns sound the 3-8 bar region in Jupiter's deep troposphere. CSHELL’s 1-arcsec -wide slit was aligned east-west on Jupiter and stepped from north to south across the NEB. Radiative transfer models indicate that the strength of the CH4 feature at 5.18 microns is anti-correlated with gaseous H2O between 3 and 6 bars. The CH4 feature is predicted to be very strong for H2O abundances less than 10ppm and it should vanish when H2O > 300ppm. Roos-Serote et al (JGR 103, 23023, 1998) retrieved a relative humidity of 0.2 of the targeted hot spot (E4FEA). When convolved to the 3800km CSHELL resolution this becomes 0.5 bars. We used the NIMS-derived H2O abundance in the hot spot to calibrate the ground-based technique. Once calibrated, the CH4 absorption feature may in turn be used to map the abundance of water in regions that Galileo/NIMS did not observe.