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The Origin of Enhanced 3He Abundances in Gradual Solar Energetic Particle Events: Evidence for Reacceleration and Jet Contributions


Core Concepts
The enhancement of 3He in gradual solar energetic particle (SEP) events is primarily caused by the reacceleration of remnant suprathermal 3He ions by CME-driven shocks, with simultaneous coronal jets potentially contributing as a significant source of energetic 3He.
Abstract
  • Bibliographic Information: Buˇc´ık, R., Hart, S. T., Dayeh, M. A., Desai, M. I., Mason, G. M., & Wiedenbeck, M. E. (2024). Origin of 3He abundance enhancements in gradual solar energetic particle events. In N. Gopalswamy, O. Malandraki, A. Vidotto & W. Manchester (Eds.), Solar and Stellar Coronal Mass Ejections: Proceedings of the IAU Symposium No. 388, 2024 (xxxxx). [Publisher name]. doi:10.1017/xxxxx
  • Research Objective: This study investigates the origin of the observed 3He abundance enhancements in gradual solar energetic particle (GSEP) events, aiming to determine the dominant contributing factors.
  • Methodology: The researchers analyzed 23 high-energy (25–50 MeV) proton events that coincided with 3He-rich periods detected by the ACE ULEIS instrument between 1997 and 2021. They examined the time profiles of 3He and 4He, calculated the 3He/4He ratios, and correlated them with the presence of coronal jets and other solar phenomena observed by SOHO ERNE, SDO AIA, and STEREO.
  • Key Findings: The analysis revealed that in most events, the 3He enhancement was likely due to the reacceleration of remnant 3He ions from preceding events or periods. Notably, a significant positive correlation was found between 3He/4He ratios and the presence of coronal jets in the parent active regions, suggesting jets as a contributing source of energetic 3He in GSEP events.
  • Main Conclusions: The study concludes that the primary mechanism behind 3He enhancements in GSEP events is the reacceleration of pre-existing suprathermal 3He populations by CME-driven shocks. However, the findings also highlight the significant role of coronal jets as a simultaneous source of energetic 3He, particularly in events with the highest 3He/4He ratios.
  • Significance: This research provides valuable insights into the complex processes of particle acceleration in the solar corona and interplanetary space. Understanding the origin and acceleration mechanisms of SEPs, particularly 3He, is crucial for space weather forecasting and mitigating the potential impacts of these particles on spacecraft and astronauts.
  • Limitations and Future Research: The study acknowledges the limitations of relying on a limited number of events and the challenges in disentangling the contributions of different source populations. Future research with larger datasets and more detailed modeling efforts is needed to further refine our understanding of 3He enhancements in GSEP events and their implications for space weather.
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Stats
The study analyzed 23 high-energy (25–50 MeV) proton events. 174 ACE ULEIS 3He-rich periods were identified between 1997 and 2021. The minimum longitudinal separation between Earth and STEREO spacecraft was 70°. The average 3He/4He ratio in the analyzed events was 26±7 times the solar wind value. The highest 3He/4He ratios were observed in events associated with coronal jets. A moderate positive correlation (r =0.593) was found between 3He/4He and Fe/O ratios.
Quotes
"Reaccelerated remnant flare material was the most probable cause of 3He enhancements in the remaining 14 proton events." "Remarkably, the highest 3He/4He occurred in events with jets, implying their contribution to 3He enhancement."

Deeper Inquiries

How do the findings of this study impact our understanding of the potential radiation hazards posed by GSEP events to astronauts and spacecraft?

This study sheds light on the origin of 3He abundance enhancements in gradual solar energetic particle (GSEP) events, which has significant implications for understanding radiation hazards in space. Here's how: Composition Matters: GSEP events, typically associated with coronal mass ejections (CMEs), are known to accelerate particles to high energies, posing a radiation risk to astronauts and spacecraft. Understanding the composition of these particles, particularly the presence of 3He, helps in developing better radiation shielding and forecasting models. Reacceleration and Enhanced Risk: The study identifies the reacceleration of remnant flare material as a major contributor to 3He enhancements in GSEPs. This means that even after a solar flare subsides, the associated CME can continue to accelerate particles to dangerous energies, prolonging the radiation hazard. Coronal Jets and Unpredictability: The study also highlights the role of coronal jets in contributing to 3He enhancements. Jets are transient events, making them harder to predict, and their contribution to GSEP composition adds another layer of complexity to radiation hazard assessment. Improved Forecasting: By understanding the different mechanisms that can lead to 3He enhancements in GSEPs, scientists can refine their models to better predict the intensity and duration of radiation storms, enabling more effective countermeasures for astronaut safety and spacecraft protection.

Could other factors besides reacceleration and coronal jets contribute to the observed 3He enhancements, and how can we investigate their potential roles?

While the study points to reacceleration and coronal jets as significant contributors to 3He enhancements, other factors could be at play. Here are some possibilities and ways to investigate them: Other Wave Modes: Besides CME-driven shocks, other wave modes like Alfvén waves could potentially contribute to particle acceleration. Analyzing in-situ observations of plasma waves during GSEP events and correlating them with 3He enhancements could provide insights. Turbulence: Turbulence in the solar corona and interplanetary space can create localized regions of enhanced magnetic fields, leading to particle acceleration. Numerical simulations and modeling of turbulence, coupled with observational data, can help assess its role in 3He enhancements. Magnetic Reconnection in Other Structures: While the study focuses on jets, magnetic reconnection in other coronal structures like coronal loops or pseudo-streamers could also contribute to 3He-rich populations. Analyzing remote sensing observations from spacecraft like SDO and STEREO can help identify such events. Pre-existing 3He-rich Reservoirs: The study acknowledges the presence of remnant 3He from previous events. Investigating the origin and characteristics of these pre-existing reservoirs, potentially through spectroscopic observations, can further our understanding.

What are the broader astrophysical implications of understanding particle acceleration mechanisms in the context of solar flares and coronal mass ejections?

Understanding particle acceleration mechanisms in solar flares and CMEs has implications beyond our solar system: Universal Processes: The processes driving particle acceleration on the Sun, like magnetic reconnection and shock acceleration, are believed to be fundamental and occur in various astrophysical environments, including: Stellar flares: Studying solar flares provides insights into the energetics and particle acceleration in flares from other stars, crucial for understanding stellar evolution and habitability. Supernova remnants: Shock waves from supernova explosions are known to accelerate particles to extremely high energies, contributing to galactic cosmic rays. Solar CME studies offer a closer look at shock acceleration physics. Active galactic nuclei: The jets launched from supermassive black holes in active galaxies are thought to be powered by processes similar to those in coronal jets, making solar studies relevant to understanding these powerful extragalactic phenomena. Cosmic Ray Origins: A significant portion of cosmic rays, high-energy particles that constantly bombard Earth, are thought to originate from our Sun. Understanding solar particle acceleration mechanisms is crucial for unraveling the sources and acceleration processes of cosmic rays, which have implications for astrobiology and the evolution of life itself. Space Weather Forecasting: As we venture further into space, understanding and predicting space weather, driven by solar flares and CMEs, becomes increasingly important. Improved knowledge of particle acceleration directly translates to better space weather forecasting, safeguarding future space missions and infrastructure.
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