Some implications of the nanoflare concept

Cargill, P. J.

doi:10.1086/173733

Cited by 255 publications

(253 citation statements)

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“…The detection of very hot plasma (T > 5 MK) in active regions, as predicted from nanoflare heating models by Cargill [13], is very significant, but requires further study with new instruments. Studies of the properties of loops, such as their widths, also provides valuable constraints on heating mechanisms [7].…”

Section: (A) Advances In Observationsmentioning

confidence: 99%

Recent advances in coronal heating

Moortel

Browning

2015

Phil. Trans. R. Soc. A.

116

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The solar corona, the tenuous outer atmosphere of the Sun, is orders of magnitude hotter than the solar surface. This 'coronal heating problem' requires the identification of a heat source to balance losses due to thermal conduction, radiation and (in some locations) convection. The review papers in this Theo Murphy meeting issue present an overview of recent observational findings, large- and small-scale numerical modelling of physical processes occurring in the solar atmosphere and other aspects which may affect our understanding of the proposed heating mechanisms. At the same time, they also set out the directions and challenges which must be tackled by future research. In this brief introduction, we summarize some of the issues and themes which reoccur throughout this issue

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Section: (A) Advances In Observationsmentioning

confidence: 99%

Recent advances in coronal heating

Moortel

Browning

2015

Phil. Trans. R. Soc. A.

116

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“…Kopp & Poletto (1993) applied a simplified point model approach, while Cargill (1994) used semi-analytic formulae. The results shown here use a 1-D hydrocode (Boris & Book 1976) that includes treatment of radiative and conductive losses (including conduction saturation) in a circular, symmetric loop (half-length L == 2 X 10 9 em and loop-top temperature T t op = 1.5 x 10 6 K).…”

Section: Introduction and Methodsmentioning

confidence: 99%

X-ray Radiation from Flare-heated Coronal Plasma

Güdel

2000

Symp. - Int. Astron. Union

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“…Cargill 1994). The relative abundances (population fractions) of the ions of a particular element are given by…”

Section: Numerical Modelmentioning

confidence: 99%

“…One example of such heating is the reconnection of adjacent magnetic field lines that have become twisted and braided in the corona due to the random motions of their photospheric footpoints. Often called nanoflares (Parker 1988;Cargill 1993Cargill , 1994Cargill 1997Klimchuk 2006), with reference to the fraction of energy released in comparison to a large scale flare, models have shown that they may heat the corona to temperatures ≥10 7 K (Cargill & Klimchuk 2004;Patsourakos & Klimchuk 2005, 2006Bradshaw & Cargill 2006;Klimchuk 2006).…”

Section: Introductionmentioning

confidence: 99%

A numerical tool for the calculation of non-equilibrium ionisation states in the solar corona and other astrophysical plasma environments

Bradshaw

2009

A&A

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Context. The effects of non-equilibrium processes on the ionisation state of strongly emitting elements in the solar corona can be extremely difficult to assess and yet they are critically important. For example, there is much interest in dynamic heating events localised in the solar corona because they are believed to be responsible for its high temperature and yet recent work has shown that the hottest (≥10 7 K) emission predicted to be associated with these events can be observationally elusive due to the difficulty of creating the highly ionised states from which the expected emission arises. This leads to the possibility of observing instruments missing such heating events entirely. Aims. The equations describing the evolution of the ionisaton state are a very stiff system of coupled, partial differential equations whose solution can be numerically challenging and time-consuming. Without access to specialised codes and significant computational resources it is extremely difficult to avoid the assumption of an equilibrium ionisation state even when it clearly cannot be justified. The aim of the current work is to develop a computational tool to allow straightforward calculation of the time-dependent ionisation state for a wide variety of physical circumstances. Methods. A numerical model comprising the system of time-dependent ionisation equations for a particular element and tabulated values of plasma temperature as a function of time is developed. The tabulated values can be the solutions of an analytical model, the output from a numerical code or a set of observational measurements. An efficient numerical method to solve the ionisation equations is implemented. Results. A suite of tests is designed and run to demonstrate that the code provides reliable and accurate solutions for a number of scenarios including equilibration of the ion population and rapid heating followed by thermal conductive cooling. It is found that the solver can evolve the ionisation state to recover exactly the equilibrium state found by an independent, steady-state solver for all temperatures, resolve the extremely small ionisation/recombination timescales associated with rapid temperature changes at high densities, and provide stable and accurate solutions for both dominant and minor ion population fractions. Rapid heating and cooling of low to moderate density plasma is characterised by significant non-equilibrium ionisation conditions. The effective ionisation temperatures are significantly lower than the electron temperature and the values found are in close agreement with the previous work of others. At the very highest densities included in the present study an assumption of equilibrium ionisation is found to be robust. Conclusions. The computational tool presented here provides a straightforward and reliable way to calculate ionisation states for a wide variety of physical circumstances. The numerical code gives results that are accurate and consistent with previous studies, has relatively undemanding computational r...

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Some implications of the nanoflare concept

Cited by 255 publications

References 0 publications

Recent advances in coronal heating

Recent advances in coronal heating

X-ray Radiation from Flare-heated Coronal Plasma

A numerical tool for the calculation of non-equilibrium ionisation states in the solar corona and other astrophysical plasma environments

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