Cooling of solar flares plasmas. 1: Theoretical considerations

Cargill, P. J.; Mariska, J. T.; Antiochos, S. K.

doi:10.1086/175240

Cited by 206 publications

(250 citation statements)

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“…As seen, the drop in the filament temperature, T SXT /T TR , by a factor of 5 results in a density reduction, n SXT /n TR , of a factor of only 1.75, i.e., during the radiation cooling, the scaling n ∝ T 0.35 holds. This rate of material leaving the radiatively cooling filament is close to the value predicted by numerical simulations (Jakimiec et al 1992;Cargill et al 1995). At this temperature and density the lifetime of SXT-detected filaments is, according to Eq.…”

Section: Implications For Nanoflaressupporting

confidence: 86%

Probing nanoflares with observed fluctuations of the coronal EUV emission

Vekstein

2009

A&A

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Context. Recent analysis of the EUV emission of the solar Active Region observed with TRACE (Sakamoto et al. 2008, ApJ, 689, 1421 revealed fluctuations which are significantly larger than the estimated photon noise and other instrumental effects. This was considered as a signature of a multiple-strand structure of coronal loops that originates from numerous sporadic coronal heating events (nanoflares). Aims. The present Letter aims to put these findings into a broader context of the nanoflare heating scenario. Methods. Simultaneous TRACE and Yohkoh/SXT observations were interpreted by using theoretical predictions of the forward modelling of the nanoflare heating. Results. It is estimated that in the coronal active region impulsive heating events have a typical energy of 10 24 erg with the average occurrence rate of 10 −17 events/cm 2 s. These could result in the hot corona with the filling factor as large as 10%. Conclusions. It is demonstrated that analysis of small fluctuations of the coronal emission can provide a useful tool for probing the mechanism of solar coronal heating.

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Section: Implications For Nanoflaressupporting

confidence: 86%

Probing nanoflares with observed fluctuations of the coronal EUV emission

Vekstein

2009

A&A

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“…Although the temporal resolution of the data is not good as compared to XRT, the spectra allow us to deduce the temperature evolution of the microflares. The observed time difference between the hot and cool emission lines is compared with a simple loop cooling model A21, page 2 of 9 by Cargill et al (1995), by analogy with large scale flares. In addition, the line ratio technique was applied to detect density enhancements in the corona, which we expected from chromospheric evaporation in the standard flare model.…”

Section: Methodsmentioning

confidence: 99%

Evolution of microflares associated with bright points in coronal holes and in quiet regions

Kamio

Curdt

Teriaca

et al. 2011

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Aims. We aim to find similarities and differences between microflares at coronal bright points found in quiet regions and coronal holes, and to study their relationship with large scale flares. Methods. Coronal bright points in quiet regions and in coronal holes were observed with Hinode/EIS using the same sequence. Microflares associated with bright points are identified from the X-ray lightcurve. The temporal variation of physical properties was traced in the course of microflares.Results. The lightcurves of microflares indicated an impulsive peak at hot emission followed by an enhancement at cool emission, which is compatible with the cooling model of flare loops. The density was found to increase at the rise of the impulsive peak, supporting chromospheric evaporation models. A notable difference is found in the surroundings of microflares; diffuse coronal jets are produced above microflares in coronal holes while coronal dimmings are formed in quiet regions. Conclusions. The microflares associated with bright points share common characteristics to active region flares. The difference in the surroundings of microflares are caused by open and closed configurations of the pre-existing magnetic field.

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“…It should be noted, nevertheless, that the cooling time-scales depend strongly on the choice of model parameters. For example, substantially denser and colder loops could reach higher values for the ratio τ cond /τ rad , or even switch from conductively cooled to radiatively cooled regimes during the course of the relaxation phase (see, e.g., Cargill 1994;Cargill et al 1995;Klimchuk et al 2008). We did not consider such cases here.…”

Section: Model Dimensions and Parametersmentioning

confidence: 99%

Soft X-ray emission in kink-unstable coronal loops

Pinto

Vilmer

Brun

2015

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Context. Solar flares are associated with intense soft X-ray emission generated by the hot flaring plasma in coronal magnetic loops. Kink-unstable twisted flux-ropes provide a source of magnetic energy that can be released impulsively and may account for the heating of the plasma in flares. Aims. We investigate the temporal, spectral, and spatial evolution of the properties of the thermal continuum X-ray emission produced in such kink-unstable magnetic flux-ropes and discuss the results of the simulations with respect to solar flare observations. Methods. We computed the temporal evolution of the thermal X-ray emission in kink-unstable coronal loops based on a series of magnetohydrodynamical numerical simulations. The numerical setup consisted of a highly twisted loop embedded in a region of uniform and untwisted background coronal magnetic field. We let the kink instability develop, computed the evolution of the plasma properties in the loop (density, temperature) without accounting for mass exchange with the chromosphere. We then deduced the X-ray emission properties of the plasma during the whole flaring episode. Results. During the initial (linear) phase of the instability, plasma heating is mostly adiabatic (as a result of compression). Ohmic diffusion takes over as the instability saturates, leading to strong and impulsive heating (up to more than 20 MK), to a quick enhancement of X-ray emission, and to the hardening of the thermal X-ray spectrum. The temperature distribution of the plasma becomes broad, with the emission measure depending strongly on temperature. Significant emission measures arise for plasma at temperatures higher than 9 MK. The magnetic flux-rope then relaxes progressively towards a lower energy state as it reconnects with the background flux. The loop plasma suffers smaller sporadic heating events, but cools down globally by thermal conduction. The total thermal X-ray emission slowly fades away during this phase, and the high-temperature component of the emission measure distribution converges to the power-law distribution EM ∝ T −4.2 . The twist deduced directly from the X-ray emission patterns is considerably lower than the highest magnetic twist in the simulated flux-ropes.

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Cooling of solar flares plasmas. 1: Theoretical considerations

Cited by 206 publications

References 0 publications

Probing nanoflares with observed fluctuations of the coronal EUV emission

Probing nanoflares with observed fluctuations of the coronal EUV emission

Evolution of microflares associated with bright points in coronal holes and in quiet regions

Soft X-ray emission in kink-unstable coronal loops

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