Modelling two energetic storm particle events observed by Solar Orbiter using the combined EUHFORIA and iPATH models

Abstract

By coupling the EUropean Heliospheric FORcasting Information Asset (EUHFORIA) and the improved Particle Acceleration and Transport in the Heliosphere (iPATH) models, we model two energetic storm particle (ESP) events originating from the same active region (AR 13088) and observed by Solar Orbiter (SolO) on August 31, 2022, and September 5, 2022. By combining numerical simulations and SolO observations, we aim to better understand particle acceleration and the transport process in the inner heliosphere. We simulated two coronal mass ejections (CMEs) in a data-driven, real-time solar wind background with the EUHFORIA code. The MHD parameters concerning the shock and downstream medium were computed from EUHFORIA as inputs for the iPATH model. In the iPATH model, a shell structure was maintained to model the turbulence-enhanced shock sheath. At the shock front, assuming diffuse shock acceleration, the particle distribution was obtained by taking the steady state solution with the instantaneous shock parameters. Upstream of the shock, particles escape, and their transport in the solar wind was described by a focused transport equation using the backward stochastic differential equation method. e n waves. The behavior of solar energetic particle (SEP) events depends on many variables. Even similar eruptions from the same AR may lead to SEP events that have very different characteristics. Simulations taking into account real-time background solar wind, the dynamics of the CME propagation, and upstream turbulence at the shock front are necessary to thoroughly understand the ESP phase of large SEP events.

Modeling Ion Acceleration and Transport in Corotating Interaction Regions: The Mass-to-charge Ratio Dependence of the Particle Spectrum

“…where k is the wavenumber; x is the position upstream of the shock and x 0 is the closest point to x on the shock; I 0 is the ambient wave intensity and a is the amplitude of enhanced wave intensity at the shock, taken to be 5 in our simulation; L, the diffusion length scale, is assumed to be 0.05 au. Note that L could be energy dependent and radial dependent, similar to the case considered at coronal mass ejection-driven shocks (Li et al 2005b(Li et al , 2021Ding et al , 2024. Upstream of the shock, I(k) reduces exponentially to the ambient level in a distance of ∼L.…”

“…To model the transport of energetic particles, a prescription of the wave intensity, which amounts to a description of particle diffusion coefficient, is needed (Wijsen et al 2021(Wijsen et al , 2023. Recently, in examining two energetic storm particle events observed by Solar Orbiter, Ding et al (2024) assumed that the wave intensity upstream of the shock decays exponentially from the shock. In this work, we follow a similar approach to describe the wave intensity upstream of the CIR shocks.…”