A contemporary view of coronal heating

Parnell, C. E.; Moortel, I. De

doi:10.1098/rsta.2012.0113

Cited by 210 publications

(192 citation statements)

References 139 publications

(247 reference statements)

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“…The footpoint motions of coronal loops result in an energy flux of ≈10 4 W m −2 and ≈10 6 W m −2 , for typical photospheric quiet-Sun and active-region conditions, respectively, to the corona. This is at least ten times larger than the corresponding radiative and conductive losses in chromosphere and corona (Bellan 2006;Parnell and De Moortel 2012).…”

Section: Energy Buildup and Storagementioning

confidence: 99%

“…The sub-surface dynamics controlling the temporal evolution of the coronal magnetic field, also launch waves propagating upwards. Currently, from all of the excited types of waves, only Alfvén waves may be capable of actually reaching coronal heights, whereas other types of waves are efficiently damped already in the low atmosphere and thus do not contribute to the heating of the coronal plasma to the observed temperatures see the recent review by Parnell and De Moortel (2012). A discussion about the corresponding coronal heating processes is outside the scope of our review and interested readers might consult also the in-depth discussion by Klimchuk (2006) and dedicated chapters in Cranmer (2009) and Reale (2010).…”

Section: Energy Buildup and Storagementioning

confidence: 99%

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The magnetic field in the solar atmosphere

Wiegelmann

Thalmann

Solanki

2014

Astron Astrophys Rev

176

125

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This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes.

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Section: Energy Buildup and Storagementioning

confidence: 99%

Section: Energy Buildup and Storagementioning

confidence: 99%

The magnetic field in the solar atmosphere

Wiegelmann

Thalmann

Solanki

2014

Astron Astrophys Rev

176

125

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“…1 The numbers of coronal null points that exist in potential magnetic field configurations, created by direct extrapolation from observed quiet-Sun regions, have been determined exactly by locating all the nulls (e.g. [9]) or estimated using a spectral method (e.g.…”

Section: Three-dimensional Coronal Topologies: Global and Localmentioning

confidence: 99%

“…The question of how the solar corona (or indeed any stellar object with a hot corona) may be heated has been considered for many decades (see [1] for a recent review) but still remains unanswered. One significant advance has been the recognition that explaining simply how the corona alone is heated is insufficient; the real question is how does the whole solar atmospheric system (the photosphere, chromosphere, transition region and corona) interact and interlink in order to sustain a hot corona?…”

Section: Introductionmentioning

confidence: 99%

Is magnetic topology important for heating the solar atmosphere?

Parnell

Stevenson

Threlfall

et al. 2015

Phil. Trans. R. Soc. A.

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Magnetic fields permeate the entire solar atmosphere weaving an extremely complex pattern on both local and global scales. In order to understand the nature of this tangled web of magnetic fields, its magnetic skeleton, which forms the boundaries between topologically distinct flux domains, may be determined. The magnetic skeleton consists of null points, separatrix surfaces, spines and separators. The skeleton is often used to clearly visualize key elements of the magnetic configuration, but parts of the skeleton are also locations where currents and waves may collect and dissipate. In this review, the nature of the magnetic skeleton on both global and local scales, over solar cycle time scales, is explained. The behaviour of wave pulses in the vicinity of both nulls and separators is discussed and so too is the formation of current layers and reconnection at the same features. Each of these processes leads to heating of the solar atmosphere, but collectively do they provide enough heat, spread over a wide enough area, to explain the energy losses throughout the solar atmosphere? Here, we consider this question for the three different solar regions: active regions, open-field regions and the quiet Sun. We find that the heating of active regions and open-field regions is highly unlikely to be due to reconnection or wave dissipation at topological features, but it is possible that these may play a role in the heating of the quiet Sun. In active regions, the absence of a complex topology may play an important role in allowing large energies to build up and then, subsequently, be explosively released in the form of a solar flare. Additionally, knowledge of the intricate boundaries of open-field regions (which the magnetic skeleton provides) could be very important in determining the main acceleration mechanism(s) of the solar wind.

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“…There have been many explanations put forward, and there are several reviews on the topic in the literature from varying perspectives (e.g., Mandrini et al 2000;Walsh & Ireland 2003;Klimchuk 2006;Reale 2010;Parnell & De Moortel 2012;Arregui 2015). Two of the most studied ideas are based on magnetic reconnection and MHD waves.…”

Section: Introductionmentioning

confidence: 99%

Measurements of Non-Thermal Line Widths in Solar Active Regions

Brooks

Warren

2016

ApJ

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Spectral line widths are often observed to be larger than can be accounted for by thermal and instrumental broadening alone. This excess broadening is a key observational constraint for both nanoflare and wave dissipation models of coronal heating. Here we present a survey of non-thermal velocities measured in the high temperature loops (1-4 MK) often found in the cores of solar active regions. This survey of Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) observations covers 15 non-flaring active regions that span a wide range of solar conditions. We find relatively small non-thermal velocities, with a mean value of 17.6 ± 5.3 km s −1 , and no significant trend with temperature or active region magnetic flux. These measurements appear to be inconsistent with those expected from reconnection jets in the corona, chromospheric evaporation induced by coronal nanoflares, and Alfvén wave turbulence models. Furthermore, because the observed non-thermal widths are generally small, such measurements are difficult and susceptible to systematic effects.

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A contemporary view of coronal heating

Cited by 210 publications

References 139 publications

The magnetic field in the solar atmosphere

The magnetic field in the solar atmosphere

Is magnetic topology important for heating the solar atmosphere?

Measurements of Non-Thermal Line Widths in Solar Active Regions

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