Ammonia and Eddy Mixing Variations in the Upper Troposphereof Jupiter from HST Faint Object Spectrograph Observations

Ultraviolet spectra of the northern and southern hemispheres of Jupiter taken with the Hubble Space Telescope Faint Object Spectrograph (FOS) in May 1992 and June 1993 have been used to derive the altitude profiles of NH3 in the vicinity of the tropopause. For a given pressure level, it is shown that the vertical profile of ammonia varies with latitude and the atmospheric feature being observed. The mixing ratio of ammonia present above the Great Red Spot (GRS) is 8× 10−8 at 250 mbar, whereas it is four times greater in the nearby South Equatorial Belt at the same pressure level. Our findings agree with those of C. A. Griffith, B. Bézard, T. Owen, and D. Gautier (1992, Icarus 98, 82–93), who find NH3 to be depleted over the GRS with respect to the South Tropical Zone at the time of the Voyager encounters. Variations of the ammonia mixing ratio in the northern and southern hemispheres are found to be nonmonotonic in latitude, indicating local dynamical effects. The observed latitudinal variation of the altitude profile of NH3 is likely to be caused by variations in the vertical eddy mixing (K),