Hybrid simulations of chromospheric HXR flare sources

Moravec, Zdeněk; Varady, M.; Kašparová, J.; Kramolis, D.

doi:10.1002/asna.201612427

Cited by 4 publications

(4 citation statements)

References 28 publications

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“…Similar behavior is seen in the evolution of heating due to electron beams in the Flarix code, as shown in e.g. Figure 2 of Moravec et al (2016). As evaporation drives the flow of plasma into the corona, the mean stopping depth is reduced and the energy deposition in the low corona begins to increase.…”

Section: Electron Beamssupporting

confidence: 68%

Electron Beams Cannot Directly Produce Coronal Rain

Reep

Antolin

Bradshaw

2020

ApJ

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Coronal rain is ubiquitous in flare loops, forming shortly after the onset of the solar flare. Rain is thought to be caused by a thermal instability, a localized runaway cooling of material in the corona. The models that demonstrate this require extremely long duration heating on the order of the radiative cooling time, localized near the footpoints of the loops. In flares, electron beams are thought to be the primary energy transport mechanism, driving strong footpoint heating during the impulsive phase that causes evaporation, filling and heating flare loops. Electron beams, however, do not act for a long period of time, and even supposing that they did, their heating would not remain localized at the footpoints. With a series of numerical experiments, we show directly that these two issues mean that electron beams are incapable of causing the formation of rain in flare loops. This result suggests that either there is another mechanism acting in flare loops responsible for rain, or that the modeling of the cooling of flare loops is somehow deficient. To adequately describe flares, the standard model must address this issue to account for the presence of coronal rain.

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Section: Electron Beamssupporting

confidence: 68%

Electron Beams Cannot Directly Produce Coronal Rain

Reep

Antolin

Bradshaw

2020

ApJ

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“…The original idea was based on an assumption that in the strong flares, the electron beams penetrate all the way down into the photosphere, where they by collisions heat the photospheric plasma, which then radiates thermally. Recent simulations (such as by Moravec et al, 2016) do not support this idea, because it seems that most of the energy in beams is deposited already at chromospheric levels and only a small fraction may propagate further down. Fletcher and Hudson (2008) suggested an alternative model in which the energy is transported from the reconnection site to the very deep layers of solar atmosphere by Alvén-wave pulses, which would provide an environment for the electrons in the lower atmosphere to be efficiently accelerated to high energies.…”

Section: White-light Flares On the Sunmentioning

confidence: 97%

Automatic detection of white-light flare kernels in SDO/HMI intensitygrams

Mravcová

Švanda

2017

New Astronomy

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Solar flares with a broadband emission in the white-light range of the electromagnetic spectrum belong to most enigmatic phenomena on the Sun. The origin of the white-light emission is not entirely understood. We aim to systematically study the visible-light emission connected to solar flares in SDO/HMI observations. We developed a code for automatic detection of kernels of flares with HMI intensity brightenings and study properties of detected candidates. The code was tuned and tested and with a little effort, it could be applied to any suitable data set. By studying a few flare examples, we found indication that HMI intensity brightening might be an artefact of the simplified procedure used to compute HMI observables.

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“…Recently, this method has also been employed in studies of the warm-target model (Jeffrey et al 2014;Kontar et al 2015) and coupled hydrodynamic simulations of solar flares (e.g. Moravec et al 2016).…”

Section: Stochastic Simulation Schemementioning

confidence: 99%

The Relation between Escape and Scattering Times of Energetic Particles in a Turbulent Magnetized Plasma: Application to Solar Flares

Effenberger¹,

Petrosian²

2018

ApJL

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A knowledge of the particle escape time from the acceleration regions of many space and astrophysical sources is of critical importance in the analysis of emission signatures produced by these particles and in the determination of the acceleration and transport mechanisms at work. This paper addresses this general problem, in particular in solar flares, where in addition to scattering by turbulence, the magnetic field convergence from the acceleration region towards its boundaries also influences the particle escape. We test an (approximate) analytic relation between escape and scattering times, and the field convergence rate, based on the work of Malyshkin and Kulsrud (2001), valid for both strong and weak diffusion limits and isotropic pitch angle distribution of the injected particles, with a numerical model of particle transport. To this end, a kinetic Fokker-Planck transport model of particles is solved with a stochastic differential equation scheme assuming different initial pitch angle distributions. This approach enables further insights into the phase-space dynamics of the transport process, which would otherwise not be accessible. We find that in general the numerical results agree well with the analytic equation for the isotropic case, however, there are significant differences weak diffusion regime for non-isotopic cases, especially for distributions beamed along the magnetic field lines. The results are important in the interpretation of observations of energetic particles in solar flares, and other similar space and astrophysical acceleration sites and for the determination of acceleration-transport coefficients, commonly used in Fokker-Planck type kinetic equations.

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Hybrid simulations of chromospheric HXR flare sources

Cited by 4 publications

References 28 publications

Electron Beams Cannot Directly Produce Coronal Rain

Electron Beams Cannot Directly Produce Coronal Rain

Automatic detection of white-light flare kernels in SDO/HMI intensitygrams

The Relation between Escape and Scattering Times of Energetic Particles in a Turbulent Magnetized Plasma: Application to Solar Flares

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