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Ilana Dashevsky (Space Telescope Science Institute), John Caldwell (York University)
HST FOS Observations at air mass 2.5 from 1800 to 2300 Å, and FOS and GHRS observations at 1.0 air mass from 1700 to 3300 Å, all at 2 degrees south latitude in the middle of a broad zone, have been used to constrain the upper stratosphere of Jupiter. The observations are reproduced well by a simple model consisting of a 15 km-am layer of H2 with Rayleigh and Raman scattering, and absorption by NH3 concentrated toward the bottom and by C2H2 concentrated toward the top. In narrow spectral regions, the model may be somewhat improved by including absorption by C4H2, C6H2 and PH3. The data do not require the presence of the polyacetylenes. In order to model the high air mass continuum at 2300 Å, it is necessary to invoke a very thin, very high-altitude layer of strongly backscattering aerosols. Contrary to expectations, NH3 was observed at the limb as well as at the center of the planet. It is important to use NH3 absorption coefficients that are measured as closely as possible to Jovian ambient conditions. Our NH3 lab sample, measured at 195 K because of vapor pressure limitations, may not have been cold enough to permit optimum interpretation of the HST data.