An analysis of the Voyager EUV spectra of the Jupiter sunlit equatorial emissions shows no evidence for a substantial dependence of atomic hydrogen abundances on magnetic longitude, required by earlier theories of the H Ly &agr; longitudinal bulge phenomenon is advanced in this work that conforms to the observations and does not reqire a strong asymmetry in atomic hydrogen abundance. It is proposed that the H Ly &agr; bulge is caused by a combination of proton collisional transfer of H(2s) atoms into the H(2p) state, and production through recombination of H+u and H+s in an asymmetric ionosphere. The asymmetry in the iono-sphere is presumably caused by Jupiter's magnetic anomaly. The processes producing the H Ly &agr; bulge require a negligible amount of directly applied energy. However, the phenomenon is a symptom of a process of substantial deposition of energy in the exosphere, forming the major source for ionospheric particles and contributing substantially to the upper atmospheric temperature. According to the present model a large fraction of the observed H Ly &agr; emission from the equatorial region is electron excited, at least at times of solar maximum. Other related phenomena and quantities required to maintain the H Ly &agr; asymmetry are discussed in the text. |