Dependence of the cutoff latitude of solar energetic protons on the southward component of the IMF

We performed simulations of the entry of solar energetic protons, at energies of 1 and 10 MeV, into the earth's magnetosphere. The proton trajectories were traced from the upstream part of the solar wind in electric and magnetic fields obtained from a global MHD simulation data. We investigated how the protons' access to high latitudes varied depending on the energy and on the interplanetary magnetic field direction. The results showed that the cutoff latitude of 1 MeV protons becomes lower when the north-south component of the interplanetary magnetic field turns from the north to the south. In contrast, the cutoff latitude of 10 MeV protons was not much affected by the change of the component.