Analysis of Jovian Auroral H Ly-α Emission (1981-1991)

Abstract

We present a new analysis of jovian auroral IUE spectra covering the period from 1981 to 1991. To extract integrated auroral H Ly-α emission from these spectra we have developed a new extraction method that bins signal with wavelength while preserving the spatial information provided by the IUE imaging spectrograph. This separates auroral emission from background sources including the jovian dayglow, geocoronal H Ly-α emission, emission from hydrogen in the interplanetary medium (IPH), and grating scattered light in the IUE spectrograph. Auroral H Ly-α emission is compared with H₂emission covering the bandpasses from 1230 to 1300 Å and 1550 to 1620 Å. Study of H₂and H Ly-α variability as a function of central meridian longitude (CML) and the results of linear correlative analysis indicates that these features are produced by a common or linked process with a similar spatial distribution. Further comparative analysis of the relative optical depth of the correlated emission using a modified form of the H₂color ratio of Yunget al.(1982,Astrophys. J.254, L65-L69) suggest that H₂and H Ly-α emissions are subject to similar variability in CH₄extinction with CML. From this a conservative upper limit of 37% is derived for the amount of H Ly-α emission that can be produced above the altitude where the bulk of the H₂emission is produced. We also discuss how the implied radiative transfer environment for H Ly-α production and the local H/CH₄ratio can limit the altitude distribution of the emission, the auroral H Ly-α intensity, and the shape and information available from the emergent line profile.