Comparison of Magnetospheric Magnetic Field Variations at Quasi-Zenith Orbit Based on Michibiki Observation and REPPU Global MHD Simulation

We compare magnetohydrodynamics (MHD) simulation results with observations from the Michibiki satellite, which is on the quasi-zenith orbit (QZO), to estimate the risk of surface charging. Surface charging results from plasma injection related to substorms. We simulated some charging events and compared the magnetic field variations causing the plasma injection. However, the magnetic field variations of simulation results tend to deviate from observations on QZO under a disturbed geomagnetic condition. We consider that the deviation under a disturbed geomagnetic condition is due to ring current enhancement in the inner magnetosphere. To produce the magnetic field variation due to ring current, we added an inner magnetospheric pressure model to the MHD simulation, which produces the ring current by artificially increasing the pressure in the inner magnetosphere. Then, we investigated the magnetic field variation causing the plasma injection. As a result, we found that the magnetic field variation causing plasma injection is reproduced in the simulation when we add the inner pressure model to the MHD simulation. This result suggests that the change in the magnetic field due to ring current in the inner magnetosphere affects the magnetic field variation of the plasma injection caused by nightside reconnection.