Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)

Dudík, J.; Dzifčáková, E.; Meyer‐Vernet, N.; Zanna, G. Del; Young, Peter R.; Giunta, A.; Sylwester, B.; Sylwester, J.; Oka, M.; Mason, H. E.; Vocks, C.; Matteini, Lorenzo; Krucker, S.; Williams, David R.; Mackovjak, Š.

doi:10.1007/s11207-017-1125-0

Cited by 78 publications

(64 citation statements)

References 376 publications

(391 reference statements)

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“…Our results indicate that surges, although traditionally described as chromospheric phenomena, show important emission in transition region lines due to the NEQ ionization linked to the quick action of the cooling processes, so the response of the transition region is intimately tied to the surge dynamics and energetics. In fact, the same statement may apply for other eruptive phenomena, in which impulsive plasma heating and cooling occurs (see Dudík et al 2017, for a review of NEQ processes in the solar atmosphere).…”

Section: On the Importance Of The Nonequilibrium (Neq) Ionizationmentioning

confidence: 80%

On the Importance of the Nonequilibrium Ionization of Si iv and O iv and the Line of Sight in Solar Surges

Nóbrega-Siverio¹,

Moreno‐Insertis²,

Martínez-Sykora³

2018

ApJ

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Surges are ubiquitous cool ejections in the solar atmosphere that often appear associated with transient phenomena like UV bursts or coronal jets. Recent observations from the Interface Region Imaging Spectrograph (IRIS) show that surges, although traditionally related to chromospheric lines, can exhibit enhanced emission in Si IV with brighter spectral profiles than for the average transition region (TR). In this paper, we explain why surges are natural sites to show enhanced emissivity in TR lines. We performed 2.5D radiative-MHD numerical experiments using the Bifrost code including the nonequilibrium ionization of silicon and oxygen. A surge is obtained as a by-product of magnetic flux emergence; the TR enveloping the emerged domain is strongly affected by nonequilibrium effects: assuming statistical equilibrium would produce an absence of Si IV and O IV ions in most of the region. Studying the properties of the surge plasma emitting in the Si IV 1402.77Å and O IV 1401.16Å lines, we find that a) the timescales for the optically-thin losses and heat conduction are very short, leading to departures from statistical equilibrium, and b) the surge emits in Si IV more and has an emissivity ratio of Si IV to O IV larger than a standard TR. Using synthetic spectra, we conclude the importance of line-of-sight effects: given the involved geometry of the surge, the line-of-sight can cut the emitting layer at small angles and/or cross it multiple times, causing prominent, spatially intermittent brightenings both in Si IV and O IV.

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Section: On the Importance Of The Nonequilibrium (Neq) Ionizationmentioning

confidence: 80%

On the Importance of the Nonequilibrium Ionization of Si iv and O iv and the Line of Sight in Solar Surges

Nóbrega-Siverio¹,

Moreno‐Insertis²,

Martínez-Sykora³

2018

ApJ

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“…Thus, it takes longer for higher-energy particles to equilibrate (e.g. Dudík et al 2017). Such an effect can be considered in an environment with density gradient (such as the solar atmosphere) to explain the origin of the non-thermal tail without resorting to wave-particle interactions (e.g.…”

Section: Fokker-planck Approachmentioning

confidence: 99%

“…Scudder and Olbert 1979). (A detailed review of non-thermal particles in a collisionally dominated non-equilibrium plasma can be found in Dudík et al (2017). )…”

Section: Fokker-planck Approachmentioning

confidence: 99%

“…There are many reviews of solar flares and associated particle acceleration (e.g. Miller et al 1997;Aschwanden 2005;Krucker et al 2008c;Lin 2011;Holman et al 2011;Petrosian 2012;Benz 2017;Dudík et al 2017). Here we focus on the power-law index measured in the sub-relativistic energy range (typically < 100 keV), as summarized in Figure 3.…”

Section: Power Laws In Solar Flaresmentioning

confidence: 99%

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Electron Power-Law Spectra in Solar and Space Plasmas

et al. 2018

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Particles are accelerated to very high, non-thermal energies in solar and space plasma environments. While energy spectra of accelerated electrons often exhibit a power law, it remains unclear how electrons are accelerated to high energies and what processes determine the power-law index δ . Here, we review previous observations of the power-law index δ in a variety of different plasma environments with a particular focus on sub-relativistic electrons. It appears that in regions more closely related to magnetic reconnection (such as the 'above-the-looptop' solar hard X-ray source and the plasma sheet in Earth's magnetotail),

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“…The principles of a numerical tool for the calculation of non-equilibrium ionisation states in the solar corona were illustrated by Bradshaw (2009), and calculations of the ionisation equilibrium timescales have been performed by several authors, such as Smith & Hughes (2010) who derived the ionisation equilibrium timescales in the absence of flows. Recently Dudík et al (2017) reviewed the state of the art for these methods. The departure from ionisation equilibrium in CME shocks for Oxygen and Silicon was justified with a numerical model by Pagano et al (2008).…”

Section: Introductionmentioning

confidence: 99%

Hydrogen non-equilibrium ionisation effects in coronal mass ejections

Pagano

Бемпорад

Mackay

2020

A&A

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Context.A new generation of coronagraphs to study the solar wind and Coronal Mass Ejections (CMEs) are being developed and launched. These coronagraphs will heavily rely on multi-channel observations where visible light (VL) and UV-EUV observations provide new plasma diagnostics. One of these instruments, Metis on board ESA-Solar Orbiter, will simultaneously observe VL and the UV Lyman-α line. The number of neutral Hydrogen atoms (a small fraction of coronal protons) is a key parameter for deriving plasma properties such as temperature from the observed Lyman-α line intensity. However, these measurements are significantly affected if non-equilibrium ionisation effects occur, which can be relevant during CMEs. Aims. The aim of this work is to determine if non-equilibrium ionisation effects are relevant in CMEs and in particular when and in which regions of the CME plasma ionisation equilibrium can be assumed for data analysis. Methods. We use a magneto-hydrodynamic simulation of a magnetic flux rope ejection to generate a CME. From this we then reconstruct the ionisation state of Hydrogen atoms in the CME by evaluating both the advection of neutral and ionised Hydrogen atoms and the ionisation and recombination rates in the MHD simulation. Results. We find that the equilibrium ionisation assumption holds mostly in the core of the CME, which is represented by a magnetic flux rope. In contrast non-equilibrium ionisation effects are significant at the CME front, where we find about 100 times more neutral Hydrogen atoms than prescribed by ionisation equilibrium conditions, even if this neutral Hydrogen excess might be difficult to identify due to projection effects. Conclusions. This work provides key information for the development of a new generation of diagnostic techniques that aim at combining visible light and Lyman-α line emissions. The results show that non-ionisation equilibrium effects need to be considered when we analyse CME fronts. To incorrectly assume equilibrium ionisation in these regions would lead to a systematic underestimate of plasma temperatures.

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Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)

Cited by 78 publications

References 376 publications

On the Importance of the Nonequilibrium Ionization of Si iv and O iv and the Line of Sight in Solar Surges

On the Importance of the Nonequilibrium Ionization of Si iv and O iv and the Line of Sight in Solar Surges

Electron Power-Law Spectra in Solar and Space Plasmas

Hydrogen non-equilibrium ionisation effects in coronal mass ejections

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