Ganymede's Auroral Footprint Latitude: Comparison With Magnetodisc Model

Variations of Ganymede's auroral footprint locations are presented based on observations by the Hubble Space Telescope in 2007 and 2016. The poleward and equatorward shifts of Ganymede's footprint could be influenced by the mass outflow rate from Io and the solar wind compression, as the internal and external factors respectively. We compare our results with Ganymede's footprint mapping based on the magnetodisc model. The mapped footprint in Jupiter's ionosphere shifts equatorward with increased hot plasma parameter, K-h, which is associated with hot plasma pressure. We analyzed the effect of cold plasma number density (N-c), related to the mass outflow rate and connected to the material produced by Io. The results show that the magnetic footprint is shifted equatorward by 0.37 degrees when the mass outflow rate is increased from 800-2,000 kg s(-1). Iogenic plasma has a strong influence on the stretching of the magnetic field lines in Jupiter's middle magnetosphere, causing the equatorward shift of Ganymede's footprint. For external factors, Ganymede's footprint shifted poleward by 0.62 degrees under the influence of solar wind compression while the mass outflow is kept constant at 1,000 kg s(-1). We present similar locations of Ganymede's footprint based on the field lines mapped as a result of the compensation between an increase of K-h and the solar wind compression. Overall, the location of Ganymede's auroral footprint corresponds with the mass loading rate from Io and the solar wind dynamic pressure.