Dynamic modeling of geomagnetic cutoff for the 23–24 November 2001 solar energetic particle event

Abstract

We investigate numerically the time variations of geomagnetic cutoffs of solar energetic particles. As a test case, the geomagnetic cutoff of 25 MeV protons is modeled for the 23–24 November 2001 solar energetic particle (SEP) event. Following Smart and Shea [2001] , solar energetic particle access is determined by computing the reverse particle trajectories. Magnetospheric fields are obtained from the Lyon‐Feder‐Mobarry (LFM) global MHD model, which is driven by measured solar wind parameters at the sunward boundary. We find well‐defined surfaces of constant cutoff that exhibit dynamic behavior in response to solar wind conditions. We show that dynamic modeling of cutoff surfaces may be used as a tool to investigate SEP access to the inner magnetosphere. The numerical results are compared with proton observations from a highly elliptical orbit (HEO) satellite. The results suggest that an enhancement in the solar wind dynamic pressure plays a role in the observed ion injection.