Particle Acceleration Processes in the Solar Corona

Melrose, D. B.

doi:10.1071/ph900703

Cited by 36 publications

(18 citation statements)

References 158 publications

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“…When a wave organizes electrons to emit in phase, the emission becomes coherent. On some cases, radio emission results from coupling two plasma waves (textbooks by Melrose 1980;Benz 2002). Coherent emissions are emitted at the local plasma frequency, upper hybrid frequency, electron gyrofrequency, or their harmonics and carry information on the plasma parameters in the source.…”

Section: Radio Emissions From the Acceleration Regionmentioning

confidence: 99%

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Flare Observations

Benz

2016

Living Rev Sol Phys

511

317

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Solar flares are observed at all wavelengths from decameter radio waves to gamma-rays beyond 1 GeV. This review focuses on recent observations in EUV, soft and hard X-rays, white light, and radio waves. Space missions such as RHESSI, Yohkoh, TRACE, SOHO, and more recently Hinode and SDO have enlarged widely the observational base. They have revealed a number of surprises: Coronal sources appear before the hard X-ray emission in chromospheric footpoints, major flare acceleration sites appear to be independent of coronal mass ejections, electrons, and ions may be accelerated at different sites, there are at least 3 different magnetic topologies, and basic characteristics vary from small to large flares. Recent progress also includes improved insights into the flare energy partition, on the location(s) of energy release, tests of energy release scenarios and particle acceleration. The interplay of observations with theory is important to deduce the geometry and to disentangle the various processes involved. There is increasing evidence supporting magnetic reconThis article is a revised version of https://doi.org/10.12942/lrsp-2008-1. Change summary Major revision, updated and expanded. Change details Significant new results from RHESSI and SDO are included. In particular, Sect. 3.4 on "Emissions from above the coronal source" was added (including two new figures) and Sect. 3.2 on "Coronal hard X-ray sources" was expanded. New observations of flares in white light are reported (replaced Fig. 25 with a movie), as well as recent multi-wavelength observations in radio waves and gamma-rays combined with hard X-rays. Four references were removed and 49 new references added. Arnold O. Benz nection as the basic cause. While this process has become generally accepted as the trigger, it is still controversial how it converts a considerable fraction of the energy into non-thermal particles. Flare-like processes may be responsible for large-scale restructuring of the magnetic field in the corona as well as for its heating. Large flares influence interplanetary space and substantially affect the Earth's ionosphere. Flare scenarios have slowly converged over the past decades, but every new observation still reveals major unexpected results, demonstrating that solar flares, after 150 years since their discovery, remain a complex problem of astrophysics including major unsolved questions. Electronic supplementary material

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Section: Radio Emissions From the Acceleration Regionmentioning

confidence: 99%

“…It is likely that more than one occurs during a flare and its secondary effects. The most widely discussed can be grouped into three types (e.g., Melrose 1990;Benz 2002):…”

Section: Electron Acceleration Theoriesmentioning

confidence: 99%

Flare Observations

Benz

2016

Living Rev Sol Phys

511

317

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“…Various preheating theories have been proposed for the solar 3He-rich events as the Ðrst stage acceleration mechanisms (for reviews see Ramaty et al 1980 ;Kocharov & Kocharov 1984 ;Mason 1987 ;Lin 1987 ;Reames 1990 ;Melrose 1990). The turbulent heating mechanism (Ibragimov & Kocharov 1977 ;Kocharov & Kocharov 1984) was disputed by Weatherall (1984) and does not work at all.…”

Section: Introductionmentioning

confidence: 99%

Solar³He‐rich Events and Electron Acceleration in Two Stages

Zhang

1999

ApJ

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The heating, acceleration, and enhancement of electrons in solar 3He-rich events are studied according to the two-stage acceleration model proposed for the enhancement of 3He and heavy ions. First, electrostatic ion cyclotron instabilities destabilized by electron currents are theoretically and numerically investigated for a plasma consisting mainly of H, 4He, and electrons. Since the parallel phase velocities of the ion cyclotron waves are smaller than around the electron thermal velocity, electrons can have strong Landau resonance with the ion cyclotron waves. Here and are, respectively, the (u r [ k A v e,A \ 0) u r k A real frequency and wavenumber parallel to the external magnetic Ðeld and is the parallel electron v e,A velocity. Second, preferential heating of electrons by the ion cyclotron waves is studied through the quasi-linear theory. It is shown that H cyclotron waves are very efficient at heating electrons through the Landau resonance. Third, these preheated electrons can be further accelerated to high energies in the Fermi acceleration process. The abundance ratio (e/H) of high-energy electrons and protons is estimated. The abundance ratio is very high when electrons are sufficiently heated relative to protons and agrees well with observations. Therefore, the present two-stage model explains all aspects of acceleration (3He, electrons, and heavy ions) in Ñares in a self-consistent way.

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“…The abundance enhancements are generally believed to result from selective heating by wave-particle interactions in the flare plasma (see reviews by Ramaty et al 1980;Kocharov & Kocharov 1984;Melrose 1990). Solar 3 He-rich events were first observed by Hsieh & Simpson (1970), and the related heavy-ion enhancements in the events were first reported by Hurford et al (1975) (see Reames 1990 and references therein).…”

Section: Introductionmentioning

confidence: 96%

Energetic-Particle Abundances in Impulsive Solar Flare Events

Reames

Meyer²,

Rosenvinge³

1994

International Astronomical Union Colloquium

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We report on the abundances of energetic particles from impulsive solar flares, including those from a survey of 228 3 He-rich events, with 3 He/ 4 He > 0.1, observed by the ISEE 3 spacecraft from 1978 August through 1991 April. The rate of occurrence of these events corresponds to ~1000 events yr -1 on the solar disk at solar maximum. Thus the resonant plasma processes that enhance 3 He and heavy elements are a common occurrence in impulsive solar flares. To supply the observed fluence of 3 He in large events, the acceleration must be highly efficient and the source region must be relatively deep in the atmosphere at a density of more than 10 10 atoms cm" 3 . 3 He/ 4 He may decrease in very large impulsive events because of depletion of 3 He in the source region.The event-to-event variations in 3 He/ 4 He, H/ 4 He, e/p, and Fe/C are uncorrected in our event sample. Abundances of the elements show a pattern in which, relative to coronal composition, 4 He, C, N, and O have normal abundance ratios, while Ne, Mg, and Si are enhanced by a factor ~2.5 and Fe by a factor ~7 . This pattern suggests that elements are accelerated from a region of the corona with an electron temperature of ~3 -5 MK, where elements in the first group are fully ionized (Q/A = 0.5), those in the second group have two orbital electrons (Q/A ~ 0.43), and Fe has Q/A ~ 0.28. Ions with the same gyrofrequency absorb waves of that frequency and are similarly accelerated and enhanced. Further stripping may occur after acceleration as the ions begin to interact with the streaming electrons that generated the plasma waves.

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Particle Acceleration Processes in the Solar Corona

Cited by 36 publications

References 158 publications

Flare Observations

Flare Observations

Solar³He‐rich Events and Electron Acceleration in Two Stages

Energetic-Particle Abundances in Impulsive Solar Flare Events

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Particle Acceleration Processes in the Solar Corona

Cited by 36 publications

References 158 publications

Flare Observations

Flare Observations

Solar3He‐rich Events and Electron Acceleration in Two Stages

Energetic-Particle Abundances in Impulsive Solar Flare Events

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Product

Resources

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Solar³He‐rich Events and Electron Acceleration in Two Stages