Case study of Ganymede’s footprint location shifts in respond with the volcanic eruptions at Io and the solar wind compression

We present here a study of the latitudinal variations of the location of Ganymede’s footprint (GFP) observed by the Hubble Space Telescope (HST) in 2007 and 2016. We assess the variation of GFP locations based on both internal and external factors, which are 1) fluctuations of the mass outflowrate (M) of the magnetospheric plasma originating from Io’s volcanic activity and 2) solar wind variations, respectively. The plasma density inside Jupiter’s magnetosphere increases due to the volcanic material on Io resulting in the stretching of magnetic field lines, which affects the equatorward shift of GFP. Meanwhile, the solar wind compression affects the decreased size of the magnetosphere, resulting in the poleward shift of GFP. Deviations of GFP location are assessed by comparison with the Ganymede mapped path by JRM33 (Connerney et al.,2022) and with the average path by Bonfond et al., 2017. We focus in particular on four epochs for which there are observations of the GFP with similar System III longitude: 1) DOY 054 and DOY 068 (February - March 2007), 2) DOY 132, DOY 154, and DOY 161 (May -
June 2007), 3) DOY 178 and DOY 199 (June - July 2016), and 4) DOY 148 and DOY 155 (May - June 2016). We compare the observation with the magnetodisc model (Nichols et al., 2015) by considering the variation of the hot plasma parameter (Kh) andMto the field line mapping in Jupiter’s ionosphere for the magnetosphere size of 80 RJ and 50 RJ (during the compression). We found that the observational results are consistent with the positions mapped by the magnetodisc model. In addition, the modelled result shows that the compression of the magnetosphere could relate to the increase ofKh in Jupiter’s magnetosphere. The results show that the shifts of GFP in case 1 and case 3 could be affected by the external factor. We also found the slightly equatorward shift in case 4 which could be dominated by the internal factor. Additionally, we presented the special event in case 2 where GFP is located in a similar location, which could be affected by the internal and the external factors at the same time.