Previous studies often assume that Jupiter’s sub-auroral ionosphere rotates with the planet, although significant deviations from corotation have been observed in the auroral regions by Stallard et al. (2001), where the line-of-sight velocities of the H_3^+ ion have shown the ionosphere to be sub-corotating. However, studies to date have not examined the line-of-sight velocities of H_3^+ at mid-to-low latitudes. At these latitudes it is thought that the H_3^+ ions will rotate with the planet as this region maps to Jupiter’s inner magnetosphere which near-rigidly corotates with the planet.
This study aims to determine whether Jupiter’s mid to low latitude ionosphere is corotating or if there is any deviation from corotation. Data for this study were obtained with the long-slit spectrometer, CSHELL, at the NASA Infrared Telescope Facility (IRTF), Hawaii. The observations of Jupiter used in this study were obtained in 1998, 2007 and 2013; each comprises several spectral images of mid and low latitudes. The line-of-sight velocities of the H_3^+ ions were derived from the Doppler shifted H_3^+ ν_2 Q(〖1,0〗^-) line at 3.953μm.
We have found that the line-of-sight velocities of the H_3^+ ions are consistent with the rigid corotation within the bounds of the experimental uncertainties. We thus confirm that the ionosphere does corotate at mid-to-low latitudes, such that the departures observed by e.g. Stallard et al. (2001) are confined to the polar region and are therefore likely to be due to magnetosphere-ionosphere coupling at those latitudes, as is often asserted.