Preliminary results from IRTF–iSHELL of Jupiter’s aurora during the NASA-Juno mission

We present a preliminary study of the H₃⁺ auroral emission at Jupiter, which uses data taken with the long-slit Echelle spectrometer, iSHELL, available at the NASA Infrared Telescope Facility (IRTF). Since first light in 2016, iSHELL has been used to provide ground-based support for the NASA-Juno mission, observing Jupiter’s aurora while Juno takes in-situ measurements of the magnetosphere as well as observing the aurora. These ground-based iSHELL measurements are critical as Juno-JIRAM lacks the spectral resolution to measure the Doppler shift of the H₃⁺ spectra, from which the line-of-sight velocity can be derived, and the ionospheric flows inferred.

Previous ground-based H₃⁺ studies have identified several significant ionospheric flows in Jupiter’s auroral region. Sub-rotating flows have been recorded in the dusk-side of the main auroral emission, which is in agreement with our current understanding of the generation of the aurora. However, super-rotating flows were also identified in the dawn-side of the main auroral emission, the origin for which remain uncertain but could lie either in driving from a dynamically changing thermosphere following a solar wind compression or the increase in angular velocity of magnetic field lines past corotation as they rotate into the dawn sector of the magnetosphere and are compressed. Furthermore, previous studies have identified a region of stationary H₃⁺ ions (relative to the magnetic pole) in the polar aurora. This stationary region was originally located coincident to the UV swirl region, however, a more recent study, using a dataset with higher spatial resolution, located the stationary region coincident with the UV dark region, which is also dark in the IR. It is thought that the stationary region is due to coupling to the solar wind either through a Dungey-like process where a single convection cell is confined by the Vasyliunas cycle or through solar wind viscous flow interaction. Therefore, the mechanisms which couple Jupiter’s aurora to the solar wind are yet to be determined.

Here we discuss the longevity and variability of the above flows using the preliminary results from the iSHELL dataset. We consider how, moving forwards, these preliminary results can be compared to Juno data to advance our understanding of the generation of Jupiter’s aurora and how it is coupled to the solar wind.