Modelling three-dimensional transport of solar energetic protons in a corotating interaction region generated with EUHFORIA

Abstract

We introduce a new solar energetic particle (SEP) transport code that aims at studying the effects of different solar wind configurations on SEP events. We focus on the influence of varying solar wind velocities on the energy changes of SEPs, and study how a non-Parker background solar wind can trap particles temporarily at small heliocentric radial distances (r<1.5 AU). Our model computes particle distributions by solving the focused transport equation (FTE) in a stochastic manner by propagating particles in a solar wind generated by the heliospheric MHD model EUHFORIA. We solve the FTE, including all solar wind effects and cross-field diffusion. As initial conditions, we inject 4 MeV protons impulsively, and spread uniformly over a selected region at the inner boundary of the model. To verify the model, we first assume nominal undisturbed fast and slow solar winds. Thereafter, we analyse the propagation of particles in a solar wind containing a corotating interaction region (CIR). The intensity-time profiles obtained in the simulations using the nominal solar winds illustrate the considerable adiabatic deceleration undergone by SEPs when propagating in a fast solar wind. For the solar wind containing a CIR, we observe particles accelerating when propagating in the compression and shock waves bounding the CIR. These waves and the magnetic configuration near the stream interface also act as a magnetic mirror, producing long-lasting high intensities at small radial distances. We also illustrate how the efficiency of the cross-field diffusion in the heliosphere is altered due to compressed magnetic fields. Finally, cross-field diffusion enables some particles to reach the forward shock wave, resulting in the formation of an accelerated particle population centred on the forward shock, despite the lack of magnetic connection between the particle injection region and this shock wave.

17 pages, 12 figures, published in Astronomy & Astrophysics

References in corpus (3)

• A Hitch-hiker's Guide to Stochastic Differential Equations: Solution Methods for Energetic Particle Transport in Space Physics and Astrophysics
• Global Numerical Modeling of Energetic Proton Acceleration in a Coronal Mass Ejection Traveling through the Solar Corona
• 3He-Rich Solar Energetic Particles in Helical Jets on the Sun

Cited by in corpus (7)

• A Primer on Focused Solar Energetic Particle Transport: Basic physics and recent modelling results
• Observation-based modelling of the energetic storm particle event of 14 July 2012
• A Self-consistent Simulation of Proton Acceleration and Transport Near a High-speed Solar Wind Stream
• On the seed population of solar energetic particles in the inner heliosphere
• The effect of drifts on the decay phase of SEP events
• Modelling the 2020 November 29 solar energetic particle event using the EUHFORIA and the iPATH model
• Interplanetary spread of solar energetic protons near a high-speed solar wind stream