On the Latitude Variation of Ammonia, Acetylene, and Phosphine Altitude Profiles on Jupiter from HST Faint Object Spectrograph Observations

Abstract

Ultraviolet spectra in the spectral region from 160 to 230 nm were taken with the Hubble Space Telescope Faint Object Spectrograph in May 1992. We analyze these data to obtain the altitude distribution of ammonia and its variation with latitude from 6°N to 25°N. Ammonia condenses below the 150-mbar level, above which it departs from saturation due to photolysis. Using a photochemical model, we also derive the value of atmospheric eddy mixing coefficients at the observed latitudes. It is found that the eddy diffusion coefficient varies from 1.5 × 10⁴cm²s^-1at 450 mbar to 4.9 × 10²cm²s^-1at 120 mbar. The vertical distribution of ammonia and the eddy diffusion coefficient do not show a large variation with latitude. We also determine an acetylene mixing ratio of (10-30) × 10^-9near 80 mbar and an upper limit of 1.5 × 10^-7for the phosphine mixing ratio, if PH₃is mixed uniformly below the 140 mbar level. The existence of particulate haze at low and high latitudes is also investigated.