31st Annual Meeting of the DPS, October 1999
Session 65. Outer Planet Atmospheres
Contributed Oral Parallel Session, Friday, October 15, 1999, 8:30-10:00am, Sala Kursaal

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[65.02] The 5-\mum absorbing clouds on Jupiter and their correlation with both visible/near-IR albedo, and far-IR radiance variations

P.G.J. Irwin, A.L. Weir, F.W. Taylor (Atmospheric, Oceanic and Planetary Physics, Oxford University), S. Franquet (Paris University), R.W. Carlson (Jet Propulsion Laboratory)

Data from the Galileo Near Infrared Mapping Spectrometer (NIMS) have been analysed to determine correlations between the observed 5-\mum brightness and the visible/near infrared albedo. A clear correlation is seen, as is expected, but the shape of the correlation spectra places strong constraints on the pressure level of the varying albedo layer. This pressure level is estimated to be greater than 1 bar and would thus appear to correspond with the cloud found by the Galileo probe Nephelometer at 1.4 bars, presumed to be composed of NH4SH, rather than the higher ammonia ice cloud at 0.7-0.5 bar.

A similar correlation study has been performed with Voyager IRIS data. Here a correlation is seen between the radiance at 5-\mum and longer wavelengths, particularly at 10 \mum and 45 \mum where the weighting functions peak at approximately 1 bar. These correlations suggest that there must be a variable opacity absorbing cloud at a pressure level less than about 0.7 bar, presumably ammonia ice, a result which at first sight is contradictory to the NIMS result.

The correlation in the radiances at 5 and 45 \mum in the IRIS data has previously been interpreted as being due entirely to the change in opacity of a cloud of ammonia particles based at 0.7 bar, with a radius 6-10 \mum. This model fits the IRIS data well but appears to be inconsistent with the new NIMS near infrared measurements. However, the IRIS results may also be modelled as being due to a small variation in opacity of larger ammonia particles at a lower pressure of 0.5-0.4 bar correlated with a large variation in opacity of the lower NH4SH cloud. This model is found to be consistent with both the NIMS reflectivity observations and the IRIS data.

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