The zonal distribution of hydrogen in the Jovian atmosphere

The Voyager ultraviolet spectrometer disclosed strong longitude variation in the midlatitude Lyman alpha brightness of Jupiter. Minimum brightness of 16 and 14.4 kR were observed from Voyagers 1 and 2, respectively, with the intensity rising to peaks of 21 and 19.6 kR at a longitude near 110°. Observations of Jovian Lyman alpha, made with the International Ultraviolet Explorer (IUE) beginning in December 1978, and continuing through January 1982, also show a region of persistently enhanced but variable flux near a longitude, λ, of 100°; however, IUE measured brightnesses are consistently lower than those of Voyager. Although the Lyman alpha flux from the “normal” region of the plant between λ 200 and 300° remained nearly constant during the period of the IUE observations, that from the “perturbed” region centered on λ 110° varied by ±25% from the mean. The sources of Lyman alpha flux include resonance scattering of solar and interplanetary Lyman alpha, and excitation by charged particle precipitation. That portion of the dayside flux due to charged particle excitation has been variously estimated at between 2.3 and 7 kR. About 1 kR of the dayside flux is due to resonance scattering of the sky background. It is assumed that H and an absorber (CH₄) are distributed above the homopause according to the local height distribution of temperature. The daytime equation of radiative transfer is solved to determine the longitudinal distribution of freely scattering atomic hydrogen that would account for the observed flux. This daytime solution shows that if the hydrogen bulge is the result of localized heating and a consequent increase in scale height, the temperature in the perturbed region must be about 100°K warmer than that in the normal region. The nightside Lyman alpha brightness exhibits a longitude variation very similar to that on the dayside. The H distribution derived from the dayside solution is used with the nightside flux to estimate the longitude variation of particle precipitation on the nightside.