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K. I. Matcheva, B. J. Conrath, P. J. Gierasch (Cornell University), F. M. Flasar (NASA/Goddard Space Flight Center)
We analyze the thermal infrared spectra of Jupiter obtained by the Cassini-CIRS instrument during the 2000 flyby to infer temperature and cloud density in the Jovian stratosphere and upper troposphere. We use an inversion technique to derive zonal mean vertical profiles of cloud absorption and cloud optical thickness from a narrow spectral window centered at 1392 cm-1. At this wavenumber the atmospheric absorption due to ammonia gas is very weak and uncertainties in the ammonia abundance do not impact the cloud retrieval results. For cloud-free conditions the optical depth of the atmosphere is of order unity at about 1200 mbar. This allows us to probe the structure of the atmosphere in a region where ammonia cloud formation is expected.
The results are presented as zonal mean contour plots of the cloud absorption and of the cloud opacity. The cloud optical thickness and the pressure of the cloud base exhibit a significant variability with latitide. In regions with a thin cloud cover the cloud absorption peaks at 1100 ±50 mbar, whereas in regions with thick clouds the peak cloud absorption occurs in the vicinity of 900 ±50 mbar. If the cloud optical thickness is too large the location of the cloud peak cannot be uniquely identified. Based on theoretical expectations for the ammonia condensation pressure we conclude that the detected clouds are probably a system of two different layers: a top ammonia ice layer at about 900 mbar covering only limited latitudes and a second deeper layer at 1100 mbar, possibly made of ammonium hydrosulfide.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.