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1. The reason for the widespread energetic storm particle event of 13 March 2023

   https://doi.org/10.1051/0004-6361/202453596  

   Dresing, N; Jebaraj, I C; Wijsen, N; Palmerio, E; Rodríguez-García, L; Palmroos, C; Gieseler, J; Jarry, M; Asvestari, E; Mitchell, J G; et al (March 2025, Astronomy & Astrophysics)

   Context.On 13 March 2023, when the Parker Solar Probe spacecraft (S/C) was situated on the far side of the Sun as seen from Earth, a large solar eruption took place, which created a strong solar energetic particle (SEP) event observed by multiple S/C all around the Sun. The energetic event was observed at six well-separated locations in the heliosphere, provided by the Parker Solar Probe, Solar Orbiter, BepiColombo, STEREO A, near-Earth S/C, and MAVEN at Mars. Clear signatures of an in situ shock crossing and a related energetic storm particle (ESP) event were observed at all inner-heliospheric S/C, suggesting that the interplanetary coronal mass ejection (CME)-driven shock extended all around the Sun. However, the solar event was accompanied by a series of pre-event CMEs. Aims.We aim to characterize this extreme widespread SEP event and to provide an explanation for the unusual observation of a circumsolar interplanetary shock and a corresponding circumsolar ESP event. Methods.We analyzed data from seven space missions, namely Parker Solar Probe, Solar Orbiter, BepiColombo, STEREO A, SOHO, Wind, and MAVEN, to characterize the solar eruption at the Sun, the energetic particle event, and the interplanetary context at each observer location as well as the magnetic connectivity of each observer to the Sun. We then employed magnetohydrodynamic simulations of the solar wind in which we injected various CMEs that were launched before as well as contemporaneously with the solar eruption under study. In particular, we tested two different scenarios that could have produced the observed global ESP event: (1) a single circumsolar blast-wave-like shock launched by the associated solar eruption, and (2) the combination of multiple CMEs driving shocks into different directions. Results.By comparing the simulations of the two scenarios with observations, we find that both settings are able to explain the observations. However, the blast-wave scenario performs slightly better in terms of the predicted shock arrival times at the various observers. Conclusions.Our work demonstrates that a circumsolar ESP event, driven by a single solar eruption into the inner heliosphere, is a realistic scenario. 

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2. An Unusual Energetic Particle Flux Enhancement Associated with Solar Wind Magnetic Island Dynamics

   Zhao, L.-L.; Zank, G.P.; Khabarova, O.; Du, S.; Chen, Y.; Adhikari, L.; Hu, Q. (September 2018, Astrophysical journal)

   The possibility that charged particles are accelerated statistically in a “sea” of small-scale interacting magnetic flux ropes in the supersonic solar wind is gaining credence. In this Letter, we extend the Zank et al. statistical transport theory for a nearly isotopic particle distribution by including an escape term corresponding to particle loss from a finite acceleration region. Steady-state 1D solutions for both the accelerated particle velocity distribution function and differential intensity are derived. We show Ulysses observations of an energetic particle flux enhancement event downstream of a shock near 5 au that is inconsistent with the predictions of classical diffusive shock acceleration (DSA) but may be explained by local acceleration associated with magnetic islands. An automated Grad-Shafranov reconstruction approach is employed to identify small-scale magnetic flux ropes behind the shock. For the first time, the observed energetic particle “time-intensity” profile and spectra are quantitatively compared with theoretical predictions. The results show that stochastic acceleration by interacting magnetic islands accounts successfully for the observed (i) peaking of particle intensities behind the shock instead of at the shock front as standard DSA predicts; (ii) increase in the particle flux amplification factor with increasing particle energy; (ii) increase in distance between the particle intensity peak and the shock front with increasing energy; and (iv) hardening of particle power-law spectra with increasing distance downstream of the shock. 

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3. An Unusual Energetic Particle Flux Enhancement Associated with Solar Wind Magnetic Island Dynamics

   Zhao, L.-L.; Zank, G. P.; Khabarova, O.; Du, S.; Chen, Y.; Adhikari, L.; Hu, Q. (September 2018, The Astrophysical journal. Letters to the editor)

   The possibility that charged particles are accelerated statistically in a “sea” of small-scale interacting magnetic flux ropes in the supersonic solar wind is gaining credence. In this Letter, we extend the Zank et al. statistical transport theory for a nearly isotopic particle distribution by including an escape term corresponding to particle loss from a finite acceleration region. Steady-state 1D solutions for both the accelerated particle velocity distribution function and differential intensity are derived. We show Ulysses observations of an energetic particle flux enhancement event downstream of a shock near 5 au that is inconsistent with the predictions of classical diffusive shock acceleration (DSA) but may be explained by local acceleration associated with magnetic islands. An automated Grad-Shafranov reconstruction approach is employed to identify small-scale magnetic flux ropes behind the shock. For the first time, the observed energetic particle “time-intensity” profile and spectra are quantitatively compared with theoretical predictions. The results show that stochastic acceleration by interacting magnetic islands accounts successfully for the observed (i) peaking of particle intensities behind the shock instead of at the shock front as standard DSA predicts; (ii) increase in the particle flux amplification factor with increasing particle energy; (ii) increase in distance between the particle intensity peak and the shock front with increasing energy; and (iv) hardening of particle power-law spectra with increasing distance downstream of the shock. 

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4. Eruption and Interplanetary Evolution of a Stealthy Streamer-Blowout CME Observed by PSP at ∼0.5 AU

   https://doi.org/10.3389/fspas.2022.903676  

   Pal, Sanchita; Lynch, Benjamin J.; Good, Simon W.; Palmerio, Erika; Asvestari, Eleanna; Pomoell, Jens; Stevens, Michael L.; Kilpua, Emilia K. (May 2022, Frontiers in Astronomy and Space Sciences)

   Streamer-blowout coronal mass ejections (SBO-CMEs) are the dominant CME population during solar minimum. Although they are typically slow and lack clear low-coronal signatures, they can cause geomagnetic storms. With the aid of extrapolated coronal fields and remote observations of the off-limb low corona, we study the initiation of an SBO-CME preceded by consecutive CME eruptions consistent with a multi-stage sympathetic breakout scenario. From inner-heliospheric Parker Solar Probe (PSP) observations, it is evident that the SBO-CME is interacting with the heliospheric magnetic field and plasma sheet structures draped about the CME flux rope. We estimate that 18 ± 11% of the CME’s azimuthal magnetic flux has been eroded through magnetic reconnection and that this erosion began after a heliospheric distance of ∼0.35 AU from the Sun was reached. This observational study has important implications for understanding the initiation of SBO-CMEs and their interaction with the heliospheric surroundings. 

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5. Modeling Particle Acceleration and Release from Solar Eruptions

   https://doi.org/10.3847/1538-4357/adcb42  

   Li, Xiaocan; Dahlin, Joel; Guo, Fan; Zhuang, Bin; Masson, Sophie; Antiochos, Spiro (May 2025, The Astrophysical Journal)

   Abstract Determining the relative contribution of solar flares versus coronal mass ejections in large solar energetic particle (SEP) events is a long-standing problem. Flare-accelerated particles may travel through complex magnetic fields in the eruption region and escape into interplanetary space, thereby contributing to large SEP events. The process by which flare accelerated particles are released into the heliosphere is poorly understood and yet is critical to advancing our understanding of SEPs. In this work, we address the release problem by solving the focused transport equation in the context of a 2.5D ARMS magnetohydrodynamic simulation of a breakout coronal mass ejection (CME)/flare event. We find that particles accelerated by flare reconnection can be released into interplanetary space through interchange reconnection between closed and open field lines. These particles can contribute directly to SEP events and may become an important seed population for further acceleration by CME-driven shocks. Additionally, we find that the energetic particle fluxes in the inner heliosphere remain elevated for an extended period, allowing them to contribute to SEP acceleration by subsequent CMEs. This study represents the first direct particle modeling of how flare-accelerated particles can contribute to major SEP events. 

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