Other
Scientific paper
Aug 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005dps....37.3022r&link_type=abstract
American Astronomical Society, DPS meeting #37, #30.22; Bulletin of the American Astronomical Society, Vol. 37, p.681
Other
Scientific paper
Models of the vertical structure of the jovian troposphere predict the existence of several cloud layers, with cloud base pressures a function of the abundance of condensibles in the atmosphere: a water cloud with a base at pressures higher then 5 bar, na ammonium hydrosulfide cloud somewhere between 1 and 2 bar and na ammonia-ice cloud near 0.7 bar. Analysis by many different authors of many different observations has not yet led to a coherent view on the vertical cloud structure inferred from these data: at visible wavelengths the cloud contrast seems to be due to a cloud located in the sub-bar region (the ammonia cloud), whereas at infrared wavelengths a cloud in the 1-2 bar region in found.
There is an unexplored region in the jovian spectrum that seems ideally suited to infer information on the vertical cloud structure: the region between 4 and 4.5 micron. This region is impossible to observe from Earth due to strong CO2 blinding and spacecraft data is also scarce: the Voyager IRIS spectra were very noisy here and the Galileo/NIMS data set does not always contain this spectral region. The region next to it, the so-called 5 micron window (4.6-5.3 micron) has been extensively studied. Radiation originates from well below the 2 bar level, being attenuated by the overlying clouds. In the 4-4.5 micron region, radiation comes from levels where the clouds are expected (1-2 bars).
We have performed a Principal Component Analysis on the entire 4-5 micron region using several NIMS data cubes. We find that about 75 % of the spatial variation is described by a first entirely positive Principal Component vector. This means that most of the variation seen in the 4-4.5 micron region has a similar origin as the variations seen in the 4.5-5.2 micron region: the opacity variations of the overying clouddeck. Yet, about 25 % is described by a second PC-vector, which shows an anti-correlation between the 4-4.5 and 4.5-5.2 micron region. We find that this can be modeled by introducing two cloud layers, one around 0.7 bar and another around 1-2 bar. We also find that the spatial variations of the opacities of these clouds must vary in an anti-correlated manner in order to reproduce the observed PCs. The physical interpretation must be linked to the way clouds are formed and the dynamics of the atmosphere.
Pimentao J.
Roos-Serote Maarten
Vicente Silvia
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