A Self-consistent Simulation of Proton Acceleration and Transport Near a High-speed Solar Wind Stream

Abstract

Solar wind stream interaction regions (SIRs) are often characterized by energetic ion enhancements. The mechanisms accelerating these particles, as well as the locations where the acceleration occurs, remain debated. Here, we report the findings of a simulation of a SIR event observed by Parker Solar Probe at ~0.56 au and the Solar Terrestrial Relations Observatory-Ahead at ~0.95 au in 2019 September when both spacecraft were approximately radially aligned with the Sun. The simulation reproduces the solar wind configuration and the energetic particle enhancements observed by both spacecraft. Our results show that the energetic particles are produced at the compression waves associated with the SIR and that the suprathermal tail of the solar wind is a good candidate to provide the seed population for particle acceleration. The simulation confirms that the acceleration process does not require shock waves and can already commence within Earth's orbit, with an energy dependence on the precise location where particles are accelerated. The three-dimensional configuration of the solar wind streams strongly modulates the energetic particle distributions, illustrating the necessity of advanced models to understand these particle events.

12 pages, 6 figures

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• On the seed population of solar energetic particles in the inner heliosphere
• Modelling the 2020 November 29 solar energetic particle event using the EUHFORIA and the iPATH model
• Cross-Field Diffusion Effects on Particle Transport in a Solar Coronal Flux Rope
• Radial Evolution of ICME-Associated Particle Acceleration Observed by Solar Orbiter and ACE
• Widespread 1-2 MeV Energetic Particles Associated with Slow and Narrow Coronal Mass Ejections: Parker Solar Probe and STEREO Measurements
• Energetic particle acceleration and transport with the novel Icarus$+$PARADISE model
• Prompt identification of solar wind stream interaction regions from Survey Burst 1 Mode observations of the Radio and Plasma Wave experiment on Solar Orbiter