Some recent developments in the theoretical dynamics of magnetic fields

Low, B. C.

doi:10.1007/bf00158434

Cited by 30 publications

(4 citation statements)

References 81 publications

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“…Accounting for projection effects, we transform the magnetic field vectors to the Heliographic coordinate system, i. e. transform the longitudinal and transverse field components to their vertical and horizontal correspondents (following Gary & Hagyard 1990). The resulting local magnetic field vectors are then preprocessed following Wiegelmann et al (2006) to gain force-free consistent boundary conditions (e. g. Aly 1984;Low 1985;Aly 1989) for the NLFF relaxation in the volume above (Wiegelmann & Inhester 2010;. A Laplace problem for the magnetic scalar potential, matching the normal component of the NLFF solution on the volumes' boundary, is solved whose gradient resembles the associated potential field solution.…”

Section: Observations and Modelingmentioning

confidence: 99%

Force-Free Field Modeling of Twist and Braiding-Induced Magnetic Energy in an Active-Region Corona

Thalmann¹,

Tiwari²,

Wiegelmann³

2013

ApJ

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The theoretical concept that braided magnetic field lines in the solar corona may dissipate a sufficient amount of energy to account for the brightening observed in the active-region corona, has been substantiated by highresolution observations only recently. From the analysis of coronal images obtained with the High Resolution Coronal Imager, first observational evidence of the braiding of magnetic field lines was reported by Cirtain et al.(2013) (hereafter CG13). We present nonlinear force-free reconstructions of the associated coronal magnetic field based on vector SDO/HMI magnetograms. We deliver estimates of the free magnetic energy associated to a braided coronal structure. Our model results suggest (∼ 100 times) more free energy at the braiding site than analytically estimated by CG13, strengthening the possibility of the active-region corona being heated by field line braiding. We were able to assess the coronal free energy appropriately by using vector field measurements and attribute the lower energy estimate of CG13 to the underestimated (by a factor of 10) azimuthal field strength. We also quantify the increase of the overall twist of a flare-related flux rope which had been claimed by CG13. From our models we find that the overall twist of the flux rope increased by about half a turn within twelve minutes. Unlike another method, to which we compare our results to, we evaluate the winding of the flux rope's constituent field lines around each other purely based on their modeled coronal 3D field line geometryto our knowledge for the first time.

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Section: Observations and Modelingmentioning

confidence: 99%

Force-Free Field Modeling of Twist and Braiding-Induced Magnetic Energy in an Active-Region Corona

Thalmann¹,

Tiwari²,

Wiegelmann³

2013

ApJ

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“…In models for coronal heating, attributed to currents generated by subphotospheric motions on a time scale less than about five minutes, reconnection is assumed to allow rapid dissipation (e.g. Low 1985). It seems inconsistent to assume that currents generated on a longer time scale lead to storage of magnetic energy building up to a flare.…”

Section: Deficiencies With Reconnection Modelsmentioning

confidence: 99%

Solar Flares: Current Dissipation or Magnetic Annihilation?

Melrose¹

1993

Aust. J. Phys.

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Solar flares involve the explosive release of energy, 1022_1025 J in 102-103 s, in the solar corona. A substantial fraction of this energy goes into energetic (~10 keY) electrons, and these produce most of the familiar signatures of flares, such as Ha emission, hard X-ray bursts and type III radio bursts. Solar flares occur in magnetic flux tubes in which the fields are highly stressed with associated large currents, I ~ 1012 A, flowing into the corona. Despite the enormous variety of detailed data on solar flares, there is no wide consensus on the essential theoretical ingredients in an acceptable flare model. Since the first detailed flare models were proposed in the 1940s, there have been two competing types: models based on an electric-current viewpoint and models based on a magnetic-field viewpoint. In principle these are equivalent, but in practice they have led to different and seemingly incompatible models. In this paper the theory of solar flares is reviewed, comparing and contrasting these two viewpoints. It is argued that all models, as presently formulated, contain serious deficiencies. One feature that is unsatisfactory is the treatment of energy propagation into a flare kernel. A specific model for such energy propagation is outlined.

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“…Since the early 1970s, an extensive study was made of force-free magnetic fields and their application to simulating coronal magnetic structures and solar flare energy buildup (e.g., see reviews by Low, 1982Low, , 1985. Vector magnetographs around the world now 12 Y. Q. Hu enable us to observe all three components of the magnetic field on the photosphere .…”

Section: Force-free Magnetic Fields and Electric Current Sheetsmentioning

confidence: 99%

Magnetic Energy Storage and Release

1991

J. geomagn. geoelec

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It is believed that magnetic energy is stored in the corona via photospheric motions in the form of force-free magnetic fields and/or electric current sheets. To produce flares, both a large storage and a fast release of magnetic free energy are needed, and they may be associated with the coexistence of a spontaneously formed electric current sheet and a highly stressed background magnetic field. The current sheet just serves as a trigger for the impulsive release of the magnetic energy stored in the high stressed field. Any fast release of magnetic energy must be accompanied with various types of MHD waves and shocks, including slow shocks and, perhaps, intermediate shocks. A realistic shock near the sun consists of several segments, which are of different types and pieced together according to certain rules, and it evolves and changes its structure while propagating outward into the interplanetary medium.

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Some recent developments in the theoretical dynamics of magnetic fields

Cited by 30 publications

References 81 publications

Force-Free Field Modeling of Twist and Braiding-Induced Magnetic Energy in an Active-Region Corona

Force-Free Field Modeling of Twist and Braiding-Induced Magnetic Energy in an Active-Region Corona

Solar Flares: Current Dissipation or Magnetic Annihilation?

Magnetic Energy Storage and Release

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