The Importance of Geometric Effects in Coronal Loop Models

Mikić, Z.; Lionello, R.; Mok, Y.; Linker, J. A.; Winebarger, Amy R.

doi:10.1088/0004-637x/773/2/94

Cited by 118 publications

(227 citation statements)

References 42 publications

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“…The heat conductivity according to Spitzer [23], q ∝ T 5/2 ∇T, is very sensitive to the temperature T. Known at least since the first one-dimensional coronal models including the transition region [24][25][26], as a consequence of the heat conductivity in the transition region the temperature gradient becomes very steep, which requires a very small grid spacing. In more recent models, the grid spacing is as small as 1 km [27] or even smaller when an adaptive grid is used [28,29]. As pointed out early in [30,31], other (turbulence) processes might take over well before such small scales for the temperature gradients are reached.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore in larger-scale three-dimensional models, the transition region cannot be resolved using Spitzer heat conduction. To cope with this problem, one can correct for the impact on the coronal pressure [27,33]. However, in the light of the above discussion comparing the electron mean-free-path length with the grid spacing, it is not clear that this is really desirable.…”

Section: Introductionmentioning

confidence: 99%

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What can large-scale magnetohydrodynamic numerical experiments tell us about coronal heating?

Peter

2015

Phil. Trans. R. Soc. A.

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The upper atmosphere of the Sun is governed by the complex structure of the magnetic field. This controls the heating of the coronal plasma to over a million kelvin. Numerical experiments in the form of threedimensional magnetohydrodynamic simulations are used to investigate the intimate interaction between magnetic field and plasma. These models allow one to synthesize the coronal emission just as it would be observed by real solar instrumentation. Largescale models encompassing a whole active region form evolving coronal loops with properties similar to those seen in extreme ultraviolet light from the Sun, and reproduce a number of average observed quantities. This suggests that the spatial and temporal distributions of the heating as well as the energy distribution of individual heat deposition events in the model are a good representation of the real Sun. This provides evidence that the braiding of fieldlines through magneto-convective motions in the photosphere is a good concept to heat the upper atmosphere of the Sun.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

What can large-scale magnetohydrodynamic numerical experiments tell us about coronal heating?

Peter

2015

Phil. Trans. R. Soc. A.

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“…We have used this model to study the plasma response to the heating into and around the moss regions. At variance with 1D models having a specified expanding cross section (Emslie et al 1992;Mikić et al 2013), we use a full MHD description, i.e., the full set of MHD equations is solved together in a 2D spatial domain; this allows us to describe a beta-changing system and to have feedback between plasma and magnetic field in the critical region, i.e., around the transition region. As a consequence, and at variance with previous works, in our model the loop cross-sectional area is also a function of time and changes as the heating changes.…”

Section: Introductionmentioning

confidence: 99%

MHD modeling of coronal loops: the transition region throat

Guarrasi

Reale

Orlando

et al. 2014

A&A

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Context. The expansion of coronal loops in the transition region may considerably influence the diagnostics of the plasma emission measure. The cross-sectional area of the loops is expected to depend on the temperature and pressure, and might be sensitive to the heating rate. Aims. The approach here is to study the area response to slow changes in the coronal heating rate, and check the current interpretation in terms of steady heating models. Methods. We study the area response with a time-dependent 2D magnetohydrodynamic (MHD) loop model, including the description of the expanding magnetic field, coronal heating and losses by thermal conduction, and radiation from optically thin plasma. We run a simulation for a loop 50 Mm long and quasi-statically heated to about 4 MK. Results. We find that the area can change substantially with the quasi-steady heating rate, e.g., by ∼40% at 0.5 MK as the loop temperature varies between 1 MK and 4 MK, and, therefore, affects the interpretation of the differential emission measure vs. temperature (DEM(T )) curves.

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“…A substantial refinement and update of these studies has been made by Mikic et al (2013) who used a 1D hydrodynamic model with variable cross-section proportional to 1/B(s), where B(s) is the magnetic field strength along the loop. Mikic et al (2013) considered the effect of varying loop parameters on the loop model solutions.…”

Section: Introductionmentioning

confidence: 99%

“…Mikic et al (2013) considered the effect of varying loop parameters on the loop model solutions. In particular, they concluded that variable cross-section area must be used for the correct derivation of densities (the modelled density at the apex was 76% larger when compared to the constant area case).…”

Section: Introductionmentioning

confidence: 99%

Diagnostics of Coronal Heating in Active-Region Loops

Fludra

Hornsey

Nakariakov

2017

ApJ

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Understanding coronal heating remains a central problem in solar physics. Many mechanisms have been proposed to explain how energy is transferred to and deposited in the corona. We summarise past observational studies that attempted to identify the heating mechanism and point out the difficulties in reproducing the observations of the solar corona from the heating models. The aim of this paper is to study whether the observed EUV emission in individual coronal loops in solar active regions can provide constraints on the volumetric heating function, and to develop a diagnostics for the heating function for a subset of loops that are found close to static thermal equilibrium. We reconstruct the coronal magnetic field from SDO/HMI data using a non-linear force free magnetic field model. We model selected loops using a 1D stationary model, with a heating rate dependent locally on the magnetic field strength along the loop, and calculate the emission from these loops in various EUV wavelengths for different heating rates. We present a method to measure a power index β defining the dependence of the volumetric heating rate E H on the magnetic field, E H ∝ B β , and controlling also the shape of the heating function: concentrated near the loop top, uniform and concentrated near the footpoints. The diagnostics is based on the dependence of the electron density on the index β. This method is free from the assumptions of the loop filling factor but requires spectroscopic measurements of the density-sensitive lines. The range of applicability for loops of different length and heating distributions is discussed, and the steps to solving the coronal heating problem are outlined.

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The Importance of Geometric Effects in Coronal Loop Models

Cited by 118 publications

References 42 publications

What can large-scale magnetohydrodynamic numerical experiments tell us about coronal heating?

What can large-scale magnetohydrodynamic numerical experiments tell us about coronal heating?

MHD modeling of coronal loops: the transition region throat

Diagnostics of Coronal Heating in Active-Region Loops

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