Resonant electrodynamic heating of stellar coronal loops - an LRC circuit analog

Ionson, J. A.

doi:10.1086/159736

Cited by 146 publications

(43 citation statements)

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“…For these low frequencies, the transition region (T.R.) acts as a transmitting and reflecting barrier, with the important property that the transmission is not symmetric, so that a coronal loop acts as a cavity that resonates at specific frequencies, based on the Alfvén crossing time t with n = 0, 1... (Ionson 1982;Hollweg 1984).…”

Section: Introductionmentioning

confidence: 99%

Coronal heating in coupled photosphere-chromosphere-coronal systems: turbulence and leakage

Verdini

Grappin

Velli

2012

A&A

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Context. Coronal loops act as resonant cavities for low-frequency fluctuations that are transmitted from the deeper layers of the solar atmosphere. These fluctuations are amplified in the corona and lead to the development of turbulence that in turn is able to dissipate the accumulated energy, thus heating the corona. However, trapping is not perfect, because some energy leaks down to the chromosphere on a long timescale, limiting the turbulent heating. Aims. We consider the combined effects of turbulence and energy leakage from the corona to the photosphere in determining the turbulent energy level and associated heating rate in models of coronal loops, which include the chromosphere and transition region. Methods. We use a piece-wise constant model for the Alfvén speed in loops and a reduced MHD-shell model to describe the interplay between turbulent dynamics in the direction perpendicular to the mean field and propagation along the field. Turbulence is sustained by incoming fluctuations that are equivalent, in the line-tied case, to forcing by the photospheric shear flows. While varying the turbulence strength, we systematically compare the average coronal energy level and dissipation in three models with increasing complexity: the classical closed model, the open corona, and the open corona including chromosphere (or three-layer model), with the last two models allowing energy leakage. Results. We find that (i) leakage always plays a role. Even for strong turbulence, the dissipation time never becomes much lower than the leakage time, at least in the three-layer model; therefore, both the energy and the dissipation levels are systematically lower than in the line-tied model; (ii) in all models, the energy level is close to the resonant prediction, i.e., assuming an effective turbulent correlation time longer than the Alfvén coronal crossing time; (iii) the heating rate is close to the value given by the ratio of photospheric energy divided by the Alfvén crossing time; (iv) the coronal spectral range is divided in two: an inertial range with 5/3 spectral slope, and a large-scale peak where nonlinear couplings are inhibited by trapped resonant modes; (v) in the realistic three-layer model, the two-component spectrum leads to a global decrease in damping equal to Kolmogorov damping reduced by a factor u rms /V c a where V c a is the coronal Alfvén speed.

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Section: Introductionmentioning

confidence: 99%

Coronal heating in coupled photosphere-chromosphere-coronal systems: turbulence and leakage

Verdini

Grappin

Velli

2012

A&A

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“…The departure to inhomogeneity typically introduces a variety of phenomena such as resonant absorption (in the corona see, e.g., Ionson 1978Ionson , 1982Ionson , 1983Hollweg 1984;Ruderman & Roberts 2002) and phase mixing (e.g. Heyvaerts & Priest 1983), all of which blur the distinction between these separate modes (see also, e.g., Bogdan et al 2003;McDougall & Hood 2007;Sousa & Cunha 2008;Cally & Hansen 2011;Hansen & Cally 2012).…”

Section: Introductionmentioning

confidence: 99%

Linear and nonlinear MHD mode coupling of the fast magnetoacoustic wave about a 3D magnetic null point

Thurgood¹,

McLaughlin²

2012

A&A

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Context. Coronal magnetic null points have been implicated as possible locations for localised heating events in 2D models. We investigate this possibility about fully 3D null points. Aims. We investigate the nature of the fast magnetoacoustic wave about a fully 3D magnetic null point, with a specific interest in its propagation, and we look for evidence of MHD mode coupling and/or conversion to the Alfvén mode. Methods. A special fieldline and flux-based coordinate system was constructed to permit the introduction of a pure fast magnetoacoustic wave in the vicinity of proper and improper 3D null points. We considered the ideal, β = 0, MHD equations, which are solved using the LARE3D numerical code. The constituent modes of the resulting wave were isolated and identified using the special coordinate system. Numerical results were supported by analytical work derived from perturbation theory and a linear implementation of the WKB method.Results. An initially pure fast wave is found to be permanently decoupled from the Alfvén mode both linearly and nonlinearly for both proper and improper 3D null points. The pure fast mode also generates and sustains a nonlinear disturbance aligned along the equilibrium magnetic field. The resulting pure fast magnetoacoustic pulse has transient behaviour, which is found to be governed by the (equilibrium) Alfvén-speed profile, and a refraction effect focuses all the wave energy towards the null point. Conclusions. Thus, the main results from previous 2D work do indeed carry over to the fully 3D magnetic null points and so we conclude that 3D null points are locations for preferential heating in the corona by 3D fast magnetoacoustic waves.

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“…m , where a is the width of an elemental magnetic loop, Re m = v A a/η D is the magnetic Reynolds number, v A is the Alfvén velocity, and η D = c 2 /4πσ is magnetic diffusivity, with σ = 1.96 ne 2 /(m e ν ei ) being the plasma conductivity (Ionson 1982;Ryutova & Habbal 1995).…”

Section: Phenomenology and Quantitative Analysismentioning

confidence: 99%

Flares Producing Well-Organized Post-Flare Arcades (Slinkies) Have Early Precursors

Ryutova¹,

Frank²,

Hagenaar³

et al. 2011

ApJ

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Exploding loop systems producing X-ray flares often, but not always, bifurcate into a long-living, well-organized system of multi-threaded loop arcades resembling solenoidal slinkies. The physical conditions that cause or prevent this process are not known. To address this problem, we examined most of the major (X-class) flares that occurred during the last decade and found that the flares that bifurcate into long-living slinky arcades have different signatures than those that do not "produce" such structures. The most striking difference is that, in all cases of slinky formation, GOES high energy proton flux becomes significantly enhanced 10-24 hr before the flare occurs. No such effect was found prior to the "non-slinky" flares. This fact may be associated with the difference between energy production by a given active region and the amount of energy required to bring the entire system into the form of wellorganized, self-similar loop arcades. As an example illustrating the process of post-flare slinky formation, we present observations taken with the Hinode satellite, in several wavelengths, showing a time sequence of pre-flare and flare activity, followed by the formation of dynamically stable, well-organized structures. One of the important features revealed is that post-flare coronal slinky formation is preceded by scale invariant structure formation in the underlying chromosphere/transition region. We suggest that the observed regularities can be understood within the framework of self-organized critical dynamics characterized by scale invariant structure formation with critical parameters largely determined by energy saturation level. The observed regularities per se may serve as a long-term precursor of strong flares and may help to study predictability of system behavior.

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Resonant electrodynamic heating of stellar coronal loops - an LRC circuit analog

Cited by 146 publications

References 0 publications

Coronal heating in coupled photosphere-chromosphere-coronal systems: turbulence and leakage

Coronal heating in coupled photosphere-chromosphere-coronal systems: turbulence and leakage

Linear and nonlinear MHD mode coupling of the fast magnetoacoustic wave about a 3D magnetic null point

Flares Producing Well-Organized Post-Flare Arcades (Slinkies) Have Early Precursors

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