Solar Energetic Proton Access to the Inner Magnetosphere during the 7-8 September 2017 event

Abstract:

The access of solar energetic protons into the inner magnetosphere on 7-8 September 2017 is investigated by following reversed proton trajectories to compute the proton cutoff energy using the Dartmouth geomagnetic cutoff code (Kress et al., 2010). The cutoff energies for protons coming from west and east direction, the minimum and maximum cutoff energy respectively, are calculated every five minutes along the orbit of the Van Allen Probes. The result shows that the cutoff energy increases significantly as the radial distance decreases, and that the cutoff energy decreases with the buildup of the ring current during the magnetic storm, with minimum Dst = - 124 nT on 8 September. A comparison is made between the use of TS07 and snapshot magnetic fields from an MHD simulation of the time interval from CME-shock arrival through Dst minimum, using the Lyon-Fedder-Mobarry code coupled with the Rice Convection Model and OMNI solar wind input. The simulation results are compared with proton flux measurements from the REPT instrument on Van Allen Probes, showing consistent variation of the cutoff location during the 7-8 September 2017 event.