Nanoflares and MHD Turbulence in Coronal Loops: A Hybrid Shell Model

Nigro, G.; Malara, F.; Carbone, V.; Veltri, P.

doi:10.1103/physrevlett.92.194501

Cited by 70 publications

(92 citation statements)

References 19 publications

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“…According to this scenario, multiscale dissipation events in the corona result from turbulent intermittency (inhomogeneous energy dissipation) associated with a cross-scale energy cascade (Boffetta et al 1999;Nigro et al 2004). The energy is initially injected at the largest scale is due to, e.g., photospheric motions.…”

Section: Routes To Multiscale Dissipationmentioning

confidence: 99%

“…Among the most important such processes are the injection of helicity associated with new magnetic structures (Falconer et al 2008;Abramenko & Yurchyshyn 2010;McAteer et al 2010;Conlon et al 2010) as well as the fragmentation of the existing magnetic flux subject to magnetic footpoint shuffling due to the turbulent photospheric convection (Lamb et al 2008;Chaouche et al 2011;Abramenko 2005). The amount of free coronal magnetic energy supplied through these processes is in a quasi-steady balance with the energy released via coronal heating and flaring activity (Simon et al 2001), possibly mediated by coronal loop turbulence and waves (Davila 1987;Ofman et al 1998;Nigro et al 2004;Buchlin et al 2005;De Pontieu et al 2007).…”

Section: Introductionmentioning

confidence: 99%

“…Coronal brightenings occurring on strongly entangled magnetic field lines tend to interact in a nonlinear fashion producing vast regions of secondary instabilities in response to relatively small triggers (Klimchuk 2006;Fuentes & Klimchuk 2010), with a noticeable fraction of magnetic discontinuities remaining silent until a local plasma instability condition is met (Vlahos & Georgoulis 2004;Aschwanden 2006). Intermittent turbulent behavior of highReynolds number photospheric and coronal flows (Abramenko et al 2002;Dmitruk & Gomez 1997;Berghmans et al 1998;Buchlin et al 2003;Nigro et al 2004;Buchlin et al 2005;Buchlin & Velli 2007;Uritsky et al 2007Uritsky et al , 2009) as well as fractal diffusion in the corona (Aschwanden 2012a) further increase the complexity of the coupling between the two solar regions.…”

Section: Introductionmentioning

confidence: 99%

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Stochastic Coupling of Solar Photosphere and Corona

Uritsky¹,

Davila²,

Ofman³

et al. 2013

ApJ

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The observed solar activity is believed to be driven by the dissipation of nonpotential magnetic energy injected into the corona by dynamic processes in the photosphere. The enormous range of scales involved in the interaction makes it difficult to track down the photospheric origin of each coronal dissipation event, especially in the presence of complex magnetic topologies. In this paper, we propose an ensemble-based approach for testing the photosphere-corona coupling in a quiet solar region as represented by intermittent activity in Solar and Heliospheric Observatory Michelson Doppler Imager and Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager image sets. For properly adjusted detection thresholds corresponding to the same degree of intermittency in the photosphere and corona, the dynamics of the two solar regions is described by the same occurrence probability distributions of energy release events but significantly different geometric properties. We derive a set of scaling relations reconciling the two groups of results and enabling statistical description of coronal dynamics based on photospheric observations. Our analysis suggests that multiscale intermittent dissipation in the corona at spatial scales >3 Mm is controlled by turbulent photospheric convection. Complex topology of the photospheric network makes this coupling essentially nonlocal and non-deterministic. Our results are in an agreement with the Parker's coupling scenario in which random photospheric shuffling generates marginally stable magnetic discontinuities at the coronal level, but they are also consistent with an impulsive wave heating involving multiscale Alfvénic wave packets and/or magnetohydrodynamic turbulent cascade. A back-reaction on the photosphere due to coronal magnetic reconfiguration can be a contributing factor.

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Section: Routes To Multiscale Dissipationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Stochastic Coupling of Solar Photosphere and Corona

Uritsky¹,

Davila²,

Ofman³

et al. 2013

ApJ

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“…They are dynamical models of the nonlinear interactions between fields on different scales and have been developed for the study of turbulence in various frameworks such as hydrodynamics (Gledzer 1973), MHD (Gloaguen et al 1985;Yamada & Ohkitani 1987), reduced MHD (Nigro et al 2004;Buchlin & Velli 2007), Hall-MHD (Galtier & Buchlin 2007), and MHD with a global rotation rate (Perrone et al 2011). A review of shell models can be found in Biferale (2003) and in the book by Bohr et al (2005).…”

Section: Introductionmentioning

confidence: 99%

Intermittent turbulent dynamo at very low and high magnetic Prandtl numbers

Buchlin

2011

A&A

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Context. Direct numerical simulations of plasmas have shown that the dynamo effect is efficient even at low Prandtl numbers, i.e., the critical magnetic Reynolds number Rm c that is necessary for a dynamo to be efficient becomes smaller than the hydrodynamic Reynolds number Re when Re → ∞. Aims. We test the conjecture that Rm c tends to a finite value when Re → ∞, and we study the behavior of the dynamo growth factor γ at very low and high magnetic Prandtl numbers. Methods. We use local and nonlocal shell models of magnetohydrodynamic (MHD) turbulence with parameters covering a much wider range of Reynolds numbers than direct numerical simulations, that is of astrophysical relevance. Results. We confirm that Rm c tends to a finite value when Re → ∞. As Rm → ∞, the limit to the dynamo growth factor γ in the kinematic regime follows Re β , and, similarly, the limit for Re → ∞ of γ behaves like Rm β , with β ≈ β ≈ 0.4. Conclusions. Our comparison with a phenomenology based on an intermittent small-scale turbulent dynamo, together with the differences between the growth rates in the different local and nonlocal models, indicate that nonlocal terms contribute weakly to the dynamo effect.

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“…In this model, shell-models of 2D MHD are coupled by Alfvén waves travelling along B 0 , and energy is only input by movements of the photospheric footpoints of the loop. This geometric setup is the same as the one used for the cellular automaton described by Buchlin et al (2003), and it gives a model similar to the one described by Nigro et al (2004). Here we use an independent implementation of these ideas to obtain the time series 3 .…”

Section: Coupled Shell-modelsmentioning

confidence: 99%

Influence of the definition of dissipative events on their statistics

Buchlin

Galtier²,

Velli³

2005

A&A

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Abstract.A convenient and widely used method to study the turbulent plasma in the solar corona is to examine statistics of properties of events (or structures) associated to flares either in observations or in numerical simulations. Numerous papers have followed such a methodology, using different definitions of an event, but the reasons behind the choice of a particular definition is very rarely discussed. We give here a comprehensive set of possible event definitions starting from a one-dimensional data set such as a time-series of energy dissipation. Each definition is then applied to a time-series of energy dissipation obtained from simulations of a shell-model of magnetohydrodynamic turbulence, or from a new model of coupled shell-models designed to represent a magnetic loop in the solar corona. We obtain distributions of the peak dissipation power, total energy, duration and waiting-time associated with each definition. These distributions are then investigated and compared, and the influence of the definition of an event on the statistics is discussed. In particular, power-law distributions are more likely to appear when using a threshold. The sensitivity of the distributions to the definition of an event seems also to be weaker for events found in a highly intermittent time series. Some implications for statistical results obtained from observations are discussed.

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Nanoflares and MHD Turbulence in Coronal Loops: A Hybrid Shell Model

Cited by 70 publications

References 19 publications

Stochastic Coupling of Solar Photosphere and Corona

Stochastic Coupling of Solar Photosphere and Corona

Intermittent turbulent dynamo at very low and high magnetic Prandtl numbers

Influence of the definition of dissipative events on their statistics

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