Thermal Non-Equilibrium Revisited: A Heating Model for Coronal Loops

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

doi:10.1088/0004-637x/773/2/134

Cited by 48 publications

(63 citation statements)

References 39 publications

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“…Thus, we extrapolate the parameter α based on a power law between α and c A in the range of 50-2000 km s −1 given by Rappazzo et al (2008) and list the values in Table A.1. Despite the wide range of Alfvén crossing times (c A covers over 4 orders of magnitude in Table A.1), the values of z are within a range of only about 0.5-1.0. Thus, using the mean of z = 0.75 (corresponding to c A = 310 km s −1 or α = 2) seems to be a good choice; this value has also been used in Lionello et al (2013) and van Wettum et al (2013). Now the exponents in Eq.…”

Section: Discussionmentioning

confidence: 99%

Scaling laws of coronal loops compared to a 3D MHD model of an active region

Bourdin

Bingert

Peter

2016

A&A

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Context. The structure and heating of coronal loops have been investigated for decades. Established scaling laws relate fundamental quantities like the loop apex temperature, pressure, length, and coronal heating. Aims. We test these scaling laws against a large-scale 3D magneto-hydrodynamics (MHD) model of the solar corona, which became feasible with current high-performance computing. Methods. We drove an active region simulation with photospheric observations and find strong similarities to the observed coronal loops in X-rays and extreme-ultraviolet (EUV) wavelength. A 3D reconstruction of stereoscopic observations shows that our model loops have a realistic spatial structure. We compared scaling laws to our model data extracted along an ensemble of field lines. Finally, we fit a new scaling law that represents hot loops and also cooler structures, which was not possible before based only on observations. Results. Our model data gives some support for scaling laws that were established for hot and EUV-emissive coronal loops. For the Rosner-Tucker-Vaiana (RTV) scaling law we find an offset to our model data, which can be explained by 1D considerations of a static loop with a constant heat input and conduction. With a fit to our model data we set up a new scaling law for the coronal heat input along magnetic field lines. Conclusions. RTV-like scaling laws were fitted to hot loops and therefore do not predict well the coronal heat input for cooler structures that are barely observable. The basic differences between 1D and self-consistent 3D modeling account for deviations between earlier scaling laws and ours. We also conclude that a heating mechanism by MHD-turbulent dissipation within a braided flux tube would heat the corona stronger than is consistent with our model corona.

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Section: Discussionmentioning

confidence: 99%

Scaling laws of coronal loops compared to a 3D MHD model of an active region

Bourdin

Bingert

Peter

2016

A&A

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“…Using this scaling law, Mok et al (2016) found a favorable comparison of forward modeled AR emission to extreme ultraviolet and soft X-Ray observations, and a particular emphasis was placed on the dynamic heating and cooling cycles (TNE) that result from such a stratified heating function (similar to what we find here). The TNE evolution was also studied in more detail along 1D loops extracted from the same simulation/field model by Lionello et al (2013) and Winebarger et al (2014).…”

Section: Scaling Of the Local Heating Ratementioning

confidence: 99%

Closed-Field Coronal Heating Driven by Wave Turbulence

Downs

Lionello

Mikić

et al. 2016

ApJ

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To simulate the energy balance of coronal plasmas on macroscopic scales, we often require the specification of the coronal heating mechanism in some functional form. To go beyond empirical formulations and to build a more physically motivated heating function, we investigate the wave-turbulence-driven (WTD) phenomenology for the heating of closed coronal loops. Our implementation is designed to capture the large-scale propagation, reflection, and dissipation of wave turbulence along a loop. The parameter space of this model is explored by solving the coupled WTD and hydrodynamic evolution in 1D for an idealized loop. The relevance to a range of solar conditions is also established by computing solutions for over one hundred loops extracted from a realistic 3D coronal field. Due to the implicit dependence of the WTD heating model on loop geometry and plasma properties along the loop and at the footpoints, we find that this model can significantly reduce the number of free parameters when compared to traditional empirical heating models, and still robustly describe a broad range of quiet-sun and active region conditions. The importance of the self-reflection term in producing relatively short heating scale heights and thermal nonequilibrium cycles is also discussed.

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“…This applies to 1D models for the dynamic evolution of loops, for example, accounting for siphon flows (Boris & Mariska 1982), in response to intermittent nanoflare heating (Hansteen 1993), or concerning catastrophic cooling (Müller et al 2003). In addition, 3D models of the coronal loop structure considered either a constant or slowly changing magnetic field in the photosphere (Gudiksen & Nordlund 2002;Bingert & Peter 2011;Lionello et al 2013). In all these models, the loops form and evolve in a preexisting coronal magnetic field above a well developed active region.…”

Section: Introductionmentioning

confidence: 99%

A model for the formation of the active region corona driven by magnetic flux emergence

Chen

Peter

Bingert

et al. 2014

A&A

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Aims. We present the first model that couples the formation of the corona of a solar active region to a model of the emergence of a sunspot pair. This allows us to study when, where, and why active region loops form, and how they evolve. Methods. We use a 3D radiation magnetohydrodynamics (MHD) simulation of the emergence of an active region through the upper convection zone and the photosphere as a lower boundary for a 3D MHD coronal model. The coronal model accounts for the braiding of the magnetic fieldlines, which induces currents in the corona to heat up the plasma. We synthesize the coronal emission for a direct comparison to observations. Starting with a basically field-free atmosphere we follow the filling of the corona with magnetic field and plasma. Results. Numerous individually identifiable hot coronal loops form, and reach temperatures well above 1 MK with densities comparable to observations. The footpoints of these loops are found where small patches of magnetic flux concentrations move into the sunspots. The loop formation is triggered by an increase in upward-directed Poynting flux at their footpoints in the photosphere. In the synthesized extreme ultraviolet (EUV) emission these loops develop within a few minutes. The first EUV loop appears as a thin tube, then rises and expands significantly in the horizontal direction. Later, the spatially inhomogeneous heat input leads to a fragmented system of multiple loops or strands in a growing envelope.

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Thermal Non-Equilibrium Revisited: A Heating Model for Coronal Loops

Cited by 48 publications

References 39 publications

Scaling laws of coronal loops compared to a 3D MHD model of an active region

Scaling laws of coronal loops compared to a 3D MHD model of an active region

Closed-Field Coronal Heating Driven by Wave Turbulence

A model for the formation of the active region corona driven by magnetic flux emergence

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