Modeling the solar energetic particle events in closed structures of interplanetary magnetic field

Abstract

We undertook a numerical modeling of the solar energetic particle (SEP) event inside a loop‐like magnetic cloud in the solar wind. Particles accelerated near the Sun are injected into the cloud of a previous coronal mass ejection (CME) that already has expanded through 1 AU. In the framework of focused transport, we perform Monte Carlo simulations of the SEP propagation and adiabatic deceleration caused by an overall expansion of the CME. The loop‐like structure of the interplanetary magnetic field strongly modifies the intensity‐time profiles of high‐energy protons. At not very small values of the particle mean free path, λ > 0.1 AU, and a power‐law energy spectrum of >1 MeV protons, the proton event development after the intensity maximum is significantly closer to an exponential‐decay profile than would be expected based on the modeling in the standard Archimedean‐spiral field. The modeling results are similar to the patterns observed with the Energetic and Relativistic Nuclei and Electron (ERNE) particle telescope on board SOHO on 2–3 May 1998. We compare the numerical modeling results with estimates based on the diffusion‐convection equation of SEP transport and provide analytical formulae, which can be used for analysis of future events.