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M. Roos-Serote (Lisbon Astron. Obs.), P. Drossart, Th. Encrenaz (Paris-Meudon Obs.), R.W. Carlson, L. Kamp (JPL)
The Near Infrared Mapping Spectrometer (NIMS) on the Galileo spacecraft continues to provide jovian atmosphere spectral images, covering wavelengths between 0.7 and 5.2 micron with a spectral resolving power of 200 at 5 micron. The spatial resolution is on the order of several hundreds of kilometers.
Here we analyze NIMS data cubes that contain spectra in Jupiter's 5-micron window. From the spectra we obtain water vapor relative humidity between 4 and 8 bar and the cloud opacity for pressures lower than about 2 bar. In addition, the overall shape of the spectra contains information on the presence or absence of cloud layers at pressures between 4 and 8 bar.
In order to fit the thousands of observed spectra, two synthetic spectral data bases were computed, containing 30,000 and 25,000 different atmospheric models respectively. They correspond to two cases : (1) a cloud layer at 1.4 bar and no clouds below, and (2) same as (1) with an extra cloud with a base at 5.5 bar.
In the second model, the level of the 5.5 bar cloud corresponds to the condensation level of water when a 2 times solar oxygen abundance is assumed. The cloud is opaque and the undersaturation of water vapor above the cloud is varied.
The comparison of the quality of the fits to the spectra using the two different models shows that the first model is much better inside the hot spots, in agreement with the Entry Probe findings. This also confirms that inside hot spots, no evidence for a water cloud is found. Outside the hot spots, the two models give similar quality of fits. We present the results of the search for clear signatures of a water cloud and regions of saturation conditions for water vapor.
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