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Universe
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Advances in Impulsive Solar Flares and Particle Acceleration
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Advances in Impulsive Solar Flares and Particle Acceleration

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Solar and Stellar Physics".

Deadline for manuscript submissions: closed (30 November 2023) | Viewed by 3120

Special Issue Editor

Dr. Yasushi Muraki

E-Mail Website
Guest Editor
Institute for Space-Earth Environment, Nagoya University, Nagoya, Japan
Interests: solar neutrons; coronal mass ejection; solar cosmic rays

Special Issue Information

Dear Colleagues,

Solar flares, characterized by the emission of gamma rays and neutrons, play a crucial role in understanding the acceleration mechanisms of ions to high energies. The time profiles of hard X-rays, in conjunction with these particles, carry valuable information regarding the ion acceleration process. Solar flares are typically classified into two categories: impulsive flares and gradual flares. While the ion acceleration process in gradual flares is believed to be associated with shock acceleration, such as in coronal mass ejections (CMEs), several unresolved aspects persist regarding the acceleration process in impulsive flares.

Observations have demonstrated that ion acceleration occurs within an extremely short timeframe (less than 1 minute), propelling ions to energies as high as 20 GeV. Phenomenologically, this acceleration process aligns with the predictions of the DC acceleration model. Therefore, in this Special Issue, we aim to present a collection of papers that delve into the essential processes involved in ion acceleration during impulsive flares.

We invite researchers to contribute their original research articles, reviews, or theoretical studies that shed light on the intricate mechanisms underlying ion acceleration in impulsive solar flares. The scope of the Special Issue encompasses a wide range of topics, including, but not limited to:

  1. Observational studies elucidating the temporal and spectral characteristics of impulsive solar flares;
  2. Theoretical models exploring the mechanisms responsible for ion acceleration during impulsive flares;
  3. Comparative analyses of ion acceleration in impulsive versus gradual flares;
  4. Investigations into the relationship between impulsive flares and other solar phenomena;
  5. Experimental and numerical studies probing the physical processes involved in ion acceleration.

We encourage authors to present novel insights, cutting-edge methodologies, and significant advancements in the field. By bringing together a diverse collection of contributions, this Special Issue aims to foster collaboration, drive innovation, and provide a comprehensive understanding of the ion acceleration process during impulsive solar flares.

We kindly invite researchers to submit their manuscripts to this Special Issue, "Impulsive Solar Flares and Particle Acceleration", in the MDPI journal Universe. We look forward to receiving your valuable contributions and making this Issue a platform for the exchange of knowledge and ideas in the field of cosmic ray physics.

Dr. Yasushi Muraki
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Further information on MDPI's Special Issue polices can be found here.

Published Papers (2 papers)

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Research

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12 pages, 1191 KiB  
Article
The 48-Year Data Analysis Collected by Nagoya Muon Telescope—A Detection of Possible (125 ± 45) Day Periodicity
by Yasushi Muraki, Shoichi Shibata, Hisanori Takamaru and Akitoshi Oshima
Universe 2023, 9(9), 387; https://doi.org/10.3390/universe9090387 - 28 Aug 2023
Cited by 1 | Viewed by 1223
Abstract
Muons produced by cosmic rays above the atmosphere provide valuable information on the intensity of cosmic rays and variations in the upper atmosphere. Since 1970, the Nagoya University Cosmic Ray Laboratory has been observing the muon intensity using a multi-directional cosmic ray telescope [...] Read more.
Muons produced by cosmic rays above the atmosphere provide valuable information on the intensity of cosmic rays and variations in the upper atmosphere. Since 1970, the Nagoya University Cosmic Ray Laboratory has been observing the muon intensity using a multi-directional cosmic ray telescope with two layers of 36 plastic scintillators of 1m2 each, which measure the muon intensity in different incident directions. The energy of an incident proton that produces a muon incident from a vertical direction is over 11.5 GV. This paper analyzes vertical muon intensities obtained over 48 years from 1970 to 2018 using methods that differ from the East–West method. As a result, a new periodicity of (125±45) days and a new periodicity of (4–16) days were found. The latter appears only in winter time, so it may be caused by a synoptic-scale disturbance associated with the arrival of the Siberian cold air mass. On the other hand, the former periodicity may be related to solar dynamo activity. In 1984, the Solar Maximum Mission’s Gamma Ray Spectrometers reported a periodicity of about (154±10) days in the flux of solar gamma rays. The (125±45)-day periodicity found here is most likely related to solar dynamo activity, since the intensity of cosmic rays around 11.5 GV is affected by the magnetic field induced by the Sun. However, this (125±45)-day periodicity differs from the report measured by the GRS instrument in a point that it also appears during periods of low solar activity. Furthermore, it has not appeared often during lower solar activity since 1992. This information is important for future investigation of the origin of this periodicity. Full article
(This article belongs to the Special Issue Advances in Impulsive Solar Flares and Particle Acceleration)
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Review

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16 pages, 2877 KiB  
Review
Element Abundances in Impulsive Solar Energetic-Particle Events
by Donald V. Reames
Universe 2023, 9(11), 466; https://doi.org/10.3390/universe9110466 - 30 Oct 2023
Cited by 4 | Viewed by 1597
Abstract
Impulsive solar energetic-particle (SEP) events were first distinguished as the streaming electrons that produce type III radio bursts as distinct from shock-induced type II bursts. They were then observed as the surprisingly enhanced 3He-rich SEP events, which were also found to have [...] Read more.
Impulsive solar energetic-particle (SEP) events were first distinguished as the streaming electrons that produce type III radio bursts as distinct from shock-induced type II bursts. They were then observed as the surprisingly enhanced 3He-rich SEP events, which were also found to have element enhancements rising smoothly with the mass-to-charge ratio A/Q through the elements, even up to Pb. These impulsive SEPs have been found to originate during magnetic reconnection in solar jets where open magnetic field lines allow energetic particles to escape. In contrast, impulsive solar flares are produced when similar reconnection involves closed field lines where energetic ions are trapped on closed loops and dissipate their energy as X-rays, γ-rays, and heat. Abundance enhancements that are power laws in A/Q can be used to determine Q values and hence the coronal source temperature in the events. Results show no evidence of heating, implying reconnection and ion acceleration occur early, rapidly, and at low density. Proton and He excesses that contribute their own power law may identify events with reacceleration of SEPs by shock waves driven by accompanying fast, narrow coronal mass ejections (CMEs) in many of the stronger jets. Full article
(This article belongs to the Special Issue Advances in Impulsive Solar Flares and Particle Acceleration)
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