19.06

The Deep Jovian Water Abundance from Remote and In Situ Observations.

A.D. Collard, L.A. Sromovsky (University of Wisconsin), G.L. Bjoraker (GSFC), G.S. Orton (JPL)

We now have three independent sources of information concerning the deep water vapour volume mixing ratio (vmr) in a Jovian North Equatorial Belt (NEB) hot spot. To the remote spectral observations in the 5 m window from the Kuiper Airbourne Observatory (Bjoraker et al., Icarus 66, 1986) and from the Voyager IRIS instrument (Kunde et al., Astrophys. J. 263, 1982; Carlson et al., JGR 98, 1993) the Galileo probe has added in situ observations by the Neutral Mass Spectrometer (NMS) (Niemann et al., Science 272, 1996) and the Net Flux Radiometer (NFR) (Sromovsky et al., ibid.) plus more spatially resolved remote sounding measurements from the Near Infrared Mapping Spectrometer (Carlson et al., Science 274, 1996).

Inverting pre-Galileo 5 m hot spot spectra to obtain water vapour profiles was an ill-defined problem. The data could be equally well explained by approximately solar water vapour abundances and thick water cloud or by substantially sub-solar water vapour abundances and no deep cloud. This ambiguity was resolved when the Galileo Probe's instruments did not detect a deep, massive water cloud (the NFR and the Nephelometer (Ragent et al., Science 274, 1996)) and found substantially sub-solar water vapour vmrs (the NFR and the NMS).

In August and December 1996, we used the NASA IRTF CSHELL instrument to obtain high resolution ( = 21500) spectra of Jupiter with a spatial resolution of 1". The aim was to observe the lines of CH (a well mixed gas) to determine the altitude of the line forming region and hence infer the opacity of the atmosphere from which the deep water vapour vmr can be inferred. Initial results from analysis of hot spot spectra are consistent with the strongly sub-solar water vapour abundances inferred by Galileo. Interestingly, the CSHELL Equatorial Zone spectra are very similar to those of the NEB Hot Spots.