Models of the ISO 3-mu m reflection spectrum of Jupiter

A spectrum of Jupiter in the 3-mu m region obtained with the Infrared Space Observatory (ISO) shows evidence for the long-sought spectral signature of NH3 ice particles in the jovian atmosphere. We calculated Jupiter 3-mu m r eflection spectrum, including multiple scattering by spherical cloud partic les. Models containing reflection from two cloud decks along with NH3 gas a bsorption reproduce the sharp drop in Jupiter's reflectance longward of 2.7 mu m. Inclusion of cloud particles composed of NH3 ice in the upper cloud near 0.55 bar improves the it to the spectrum near 3.0 mu m, due to the N-H stretch absorption of solid NH3. For models with a single size for the NH3 ice, particles with radius a approximate to 10 mu m give the best fit. For a model with a bimodal distribution of a = 1 mu m and a = 10 mu m NH3 ice particles, the large particles need to dominate the 3-mu m NH3 ice particle opacity to provide absorption that is sufficiently broad. (C) 1998 Academi c Press.