Jupiter's dayglow H Ly α emission line profile

IUE spectra of Jupiter's low latitude H Ly α emission line profile have been obtained on and off the “Ly α bulge” at the longitude of the central meridian (CML), near the limb of the planet, and at midlatitudes on the CML. All equatorial locations show line broadening beyond the IUE resolution of 0.14 Å. The equatorial lines are significantly broader than at midlatitudes on the CML, and near the limb the lines are broader than on the CML, both on and off the bulge. The observed line shapes are not consistent with pure resonant scattering of solar Ly α by upper atmospheric H atoms with a variable H abundance: calculated profiles near the limb have much less intense cores. The broadening of the bulge line profiles on the CML and limb compared with off‐bulge regions demonstrates that the bulge effect is a broadening of the line, not an increase in the line core flux. We propose that there is either a substantial broadened internal source and/or the upper atmosphere has considerable Doppler broadening (winds or turbulence) to increase the resonant scattering line width.