Role of Suprathermal Runaway Electrons Returning to the Acceleration Region in Solar Flares

AbstractThis article focuses on two problems involved in the development of models of solar flares. The first concerns the mechanism responsible for eruptions, such as erupting filaments or coronal mass ejections, that are sometimes involved in the flare process. The concept of ‘loss of equilibrium’ is considered and it is argued that the concept typically arises in thought-experiments that do not represent acceptable physical behavior of the solar atmosphere. It is proposed instead that such eruptions are probably caused by an instability of a plasma configuration. The instability may be purely MHD, or it may combine both MHD and resistive processes. The second problem concerns the mechanism of energy release of the impulsive (or gradual) phase. It is proposed that this phase of flares may be due to current interruption, as was originally proposed by Alfvén and Carlqvist. However, in order for this process to be viable, it seems necessary to change one's ideas about the heating and structure of the corona in ways that are outlined briefly.

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Mechanisms for Flash Phase Phenomena in Solar Flares

Symposium - International Astronomical Union ◽

10.1017/s0074180900234335 ◽

1974 ◽

Vol 57 ◽

pp. 253-282 ◽

Cited By ~ 1

Author(s):

Dean F. Smith

Keyword(s):

Solar Flares ◽

Acoustic Waves ◽

Plasma Waves ◽

Electron Plasma ◽

X Rays ◽

Fermi Acceleration ◽

Acceleration Region ◽

Low Frequencies ◽

Coulomb Collisions ◽

The Earth

Mechanisms for explaining the various forms of particles and radiation observed during the flash phase of solar flares are reviewed under the working hypothesis that the flash phase is the time in which electrons and to a lesser degree protons are accelerated in less than one second. A succession of such accelerations is allowed to explain longer lasting or quasi-periodic phenomena. Mechanisms capable of such acceleration are reviewed and it is concluded that first-order Fermi acceleration in a reconnecting current sheet is the most likely basic process. Such acceleration, however, gives rise to a rather narrow distribution of particle velocities along a given field line which is unstable to the production of electron plasma and ion-acoustic waves. This plasma turbulence can heat the plasma to produce soft X-rays and filter the initially narrow velocity distribution to produce a power law energy distribution. Electrons travelling inward from the acceleration region produce hard X-rays by bremsstrahlung and microwave bursts by gyro-synchrotron emission. Whereas the interpretation of X-ray spectra is relatively straightforward, the interpretation of microwave spectra is difficult because the source at low frequencies can be made optically thick by several different mechanisms.Electrons travelling further inward presumably thermalize and produce impulsive EUV and Hα emission. The theory for these emissions, although amenable to present techniques in radiative transfer, has not been worked out. Electrons travelling outward give rise to type III radio bursts by excitation of electron plasma waves and the electrons observed at the Earth. Study of the interaction of a stream of electrons with the ambient plasma shows that the electron spectra observed at the Earth do not necessarily reflect their spectrum at the acceleration region since they interact via plasma waves as well as through Coulomb collisions. The mechanisms for the conversion of plasma waves into radiation and the propagation of the radiation from its source to the observer are reviewed.

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The Role of Magnetic Helicity in Solar Flares

Highlights of Astronomy ◽

10.1017/s1539299600015318 ◽

2005 ◽

Vol 13 ◽

pp. 128-131

Author(s):

Mark G. Linton

Keyword(s):

Solar Flares ◽

Magnetic Energy ◽

Active Regions ◽

Excess Energy ◽

Flux Tubes ◽

Surplus Energy ◽

Coronal Magnetic Fields ◽

Kink Instability ◽

Magnetic Energy Release

AbstractHelicity in coronal magnetic fields, often occurring in the form of twisted or sheared fields, can provide surplus energy which is available for release in solar flares. In this paper, several models of how this extra, non-potential, energy can be released will be reviewed. For example, twisted flux tubes can release excess energy via the kink instability. Or energy can be released via a transfer of helicity between different magnetic tubes. For untwisted field, the mutual helicity between flux tubes provides a measure of the shear in the fields, and therefore how much energy is available for release in a flare. For twisted flux tubes, the twist helicity of each tube in combination with the mutual helicity between the tubes dictate what type of reconnection the tubes can undergo and how much energy is available for release. Measuring the helicity of coronal active regions, and studying how this helicity affects magnetic energy release is therefore vital for our understanding of and our ability to predict solar flares.

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Solar flare forecasting model using 3D magnetic field data

10.5194/egusphere-egu2020-13298 ◽

2020 ◽

Author(s):

Xin Huang

Keyword(s):

Magnetic Field ◽

Deep Learning ◽

Solar Flare ◽

Solar Flares ◽

Field Data ◽

Active Regions ◽

Forecasting Model ◽

Magnetic Field Data ◽

The Magnetic Field

<p>Solar flares originate from the release of the energy stored in the magnetic field of solar active regions. Generally, the photospheric magnetograms of active regions are used as the input of the solar flare forecasting model. However, solar flares are considered to occur in the low corona. Therefore, the role of 3D magnetic field of active regions in the solar flare forecast should be explored. We extrapolate the 3D magnetic field using the potential model for all the active regions during 2010 to 2017, and then the deep learning method is applied to extract the precursors of solar flares in the 3D magnetic field data. We find that the 3D magnetic field of active regions is helpful to build a deep learning based forecasting model.</p>

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