Jovian Auroral Lyalpha Self-Reversals: A Window on Jupiter's Auroral Electrojet?

High-resolution GHRS profiles of Lyalpha lines emitted from Jupiter's auroral regions were presented by Prang{e} et al. (Astrophys. J., 484, L169--L173, 1997). Their data show asymmetric self-reversed line profiles, with the blue or red peak brighter depending on the target location in Jupiter's northern auroral region. The measured asymmetries are equivalent to Doppler velocities towards and away from the observer of several km/s. As suggested by Sommeria et al. (Icarus, 119, 2--24, 1995), electrojet velocities of ~ 10--20 km/s may be present at Jupiter. Here we investigate the possibility that the observed wavelength shifts of the auroral Lyalpha line are a result of multiple scattering by H atoms carried along in Jupiter's auroral electrojet. If this explanation is found to be viable, then HST/STIS mapping of the velocity shifts in the Lyalpha line may represent (as with ground-based high-resolution observations of jovian auroral H_3(+) emission lines) a means for determining the dynamics of Jupiter's upper atmosphere and ionosphere.