Fresh ammonia ice clouds in Jupiter - I. Spectroscopic identification, spatial distribution, and dynamical implications

We report the first spectroscopic detection of discrete ammonia ice clouds in the atmosphere of Jupiter, as discovered utilizing the Galileo Near-Infrared Mapping Spectrometer (NIMS). Spectrally identifiable ammonia clouds (SIACs) cover less than 1% of the globe, as measured in complete global imagery obtained in September 1996 during Galileo's second orbit. More than half of the most spectrally prominent SIACs reside within a small latitudinal band, extending from 2degrees to 7degrees N latitude, just south of the 5-mum hot spots. The most prominent of these are spatially correlated with nearby 5-mum-bright hot spots lying 1.5degrees-3.0degrees of latitude to the north: they reside over a small range of relative longitudes on the eastward side of hot spots, about 37% of the longitudinal distance to the next hot spot to the east. This strong correlation between the positions of hot spots and the most prominent equatorial SIACs suggests that they are linked by a common planetary wave. Good agreement is demonstrated between regions of condensation predicted by the Rossby wave model of A. J. Friedson and G. S. Orton (1999, Bull. Am. Astron. Assoc 31, 1155-1156) and the observed longitudinal positions of fresh ammonia clouds relative to 5-mum hot spots. Consistency is also demonstrated between (1) the lifetime of particles as determined by the wave phase speed and cloud width and (2) the sedimentation time for 10-mum radius particles consistent with previously reported ammonia particle size by T. Y. Brooke et al. (1998, Icarus 136, 1-13). A young age (