Entropy mode at a magnetic null point as a possible tool for indirect observation of nanoflares in the solar corona

Murawski, K.; Zaqarashvili, T. V.; Nakariakov, V. M.

doi:10.1051/0004-6361/201116942

Cited by 34 publications

(35 citation statements)

References 33 publications

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“…Temperatures with peak at 20,000 K and plasma-β values of maximum 0.557, were found, both within ranges already reported (Ahn et al, 2014;Shimojo et al, 2002), (Antolin & Verwichte, 2011). Regarding our findings on the magneto-acoustic wave, Murawski et al (2011) also found that magnetoacoustic waves were linked to cool dense descending blobs, while Oliver et al (2014) supports that down falling blobs emit small amplitude sound waves of periods of about 100s. It must be stated that our magnetic field strength resembles more that of quiet Sun, rather than an active region case.…”

Section: Discussionsupporting

confidence: 91%

Simulating coronal condensation dynamics in 3D

Moschou

Keppens

Xia

et al. 2015

Advances in Space Research

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We present numerical simulations in 3D settings where coronal rain phenomena take place in a magnetic configuration of a quadrupolar arcade system. Our simulation is a magnetohydrodynamic simulation including anisotropic thermal conduction, optically thin radiative losses, and parametrised heating as main thermodynamical features to construct a realistic arcade configuration from chromospheric to coronal heights. The plasma evaporation from chromospheric and transition region heights eventually causes localised runaway condensation events and we witness the formation of plasma blobs due to thermal instability, that evolve dynamically in the heated arcade part and move gradually downwards due to interchange type dynamics. Unlike earlier 2.5D simulations, in this case there is no large scale prominence formation observed, but a continuous coronal rain develops which shows clear indications of Rayleigh-Taylor or interchange instability, that causes the denser plasma located above the transition region to fall down, as the system moves towards a more stable state. Linear stability analysis is used in the non-linear regime for gaining insight and giving a prediction of the system's evolution. After the plasma blobs descend through interchange, they follow the magnetic field topology more closely in the lower coronal regions, where they are guided by the magnetic dips.Comment: 47 pages, 59 figure

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Section: Discussionsupporting

confidence: 91%

Simulating coronal condensation dynamics in 3D

Moschou

Keppens

Xia

et al. 2015

Advances in Space Research

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“…Ref. 33 and references therein, for the description of the physical properties of the latter, which are out of the scope of this study). Previous theoretical estimations 14,34 show that the characteristic time scale of the thermal conduction is highly sensitive to the equilibrium temperature and density of the plasma and to the wavelength of the oscillation, λ,…”

Section: Dispersion Relation and Characteristic Time Scalesmentioning

confidence: 99%

Formation of quasi-periodic slow magnetoacoustic wave trains by the heating/cooling misbalance

et al. 2019

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Slow magnetoacoustic waves are omnipresent in both natural and laboratory plasma systems. The wave-induced misbalance between plasma cooling and heating processes causes the amplification or attenuation, and also dispersion, of slow magnetoacoustic waves. The wave dispersion could be attributed to the presence of characteristic time scales in the system, connected with the plasma heating or cooling due to the competition of the heating and cooling processes in the vicinity of the thermal equilibrium. We analysed linear slow magnetoacoustic waves in a plasma in a thermal equilibrium formed by a balance of optically thin radiative losses, field-align thermal conduction, and an unspecified heating. The dispersion is manifested by the dependence of the effective adiabatic index of the wave on the wave frequency, making the phase and group speeds frequency-dependent. The mutual effect of the wave amplification and dispersion is shown to result into the occurrence of an oscillatory pattern in an initially broadband slow wave, with the characteristic period determined by the thermal misbalance time scales, i.e. by the derivatives of the combined radiation loss and heating function with respect to the density and temperature, evaluated at the equilibrium. This effect is illustrated by estimating the characteristic period of the oscillatory pattern, appearing because of thermal misbalance in the plasma of the solar corona. It is found that by an order of magnitude the period is about the typical periods of slow magnetoacoustic oscillations detected in the corona.

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“…(3) also excites slow and entropy modes (Murawski et al 2011). However, in this study we focus on the time interval associated with the development of fast magnetoacoustic waves.…”

Section: Numerical Modellingmentioning

confidence: 99%

Observation of a high-quality quasi-periodic rapidly propagating wave train using SDO/AIA

Nisticò

Pascoe

Nakariakov

2014

A&A

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Context. We present a new event of quasi-periodic wave trains observed in EUV wavebands that rapidly propagate away from an active region after a flare. Aims. We measured the parameters of a wave train observed on 7 December 2013 after an M1.2 flare, such as the phase speeds, periods and wavelengths, in relationship to the local coronal environment and the energy sources. Methods. We compared our observations with a numerical simulation of fast magnetoacoustic waves that undergo dispersive evolution and leakage in a coronal loop embedded in a potential magnetic field. Results. The wave train is observed to propagate as several arc-shaped intensity disturbances for almost half an hour, with a speed greater than 1000 km s −1 and a period of about 1 min. The wave train followed two different patterns of propagation, in accordance with the magnetic structure of the active region. The oscillatory signal is found to be of high-quality, i.e. there is a large number (10 or more) of subsequent wave fronts observed. The observations are found to be consistent with the numerical simulation of a fast wave train generated by a localised impulsive energy release. Conclusions. Transverse structuring in the corona can efficiently create and guide high-quality quasi-periodic propagating fast wave trains.

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Entropy mode at a magnetic null point as a possible tool for indirect observation of nanoflares in the solar corona

Cited by 34 publications

References 33 publications

Simulating coronal condensation dynamics in 3D

Simulating coronal condensation dynamics in 3D

Formation of quasi-periodic slow magnetoacoustic wave trains by the heating/cooling misbalance

Observation of a high-quality quasi-periodic rapidly propagating wave train using SDO/AIA

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