Reconnection‐Driven Dynamics at Ganymede’s Upstream Magnetosphere: 3‐D Global Hall MHD and MHD‐EPIC Simulations

The largest moon in the solar system, Ganymede, is the only moon known to possess a strong intrinsic magnetic field and a corresponding magnetosphere. Using the latest version of Space Weather Modeling Framework (SWMF), we study the upstream plasma interactions and dynamics in this sub‐Alfvénic system. Results from the Hall magnetohydrodynamics (MHD) and the coupled MHD with embedded particle‐in‐cell (MHD‐EPIC) models are compared. We find that under steady upstream conditions, magnetopause reconnection occurs in a nonsteady manner, and the energy partition between electrons and ions is different in the two models. Flux ropes of Ganymede’s radius in length form on the magnetopause at a rate about 3 min and create spatiotemporal variations in plasma and field properties. Upon reaching proper grid resolutions, the MHD‐EPIC model can resolve both electron and ion kinetics at the magnetopause and show localized nongyrotropic behavior inside the diffusion region. The estimated global reconnection rate from the models is about 80 kV with 60% efficiency, and there is weak evidence of ∼1 min periodicity in the temporal variations due to the dynamic reconnection process.Key PointsSimulated flux rope of the length of Ganymede’s radius forms at a rate of ∼2 min at the upstream magnetopauseIon and electron scale kinetic physics near the reconnection site are revealed with coupled kinetic modelA general and robust method to measure the global reconnection rate is proposedPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156495/3/jgra55850_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156495/2/jgra55850.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156495/1/jgra55850-sup-0001-Supporting_Information_SI-S01.pd