Force‐Freeness of Solar Magnetic Fields in the Photosphere

Moon, Y.-J.; Choe, G. S.; Yun, Hong Sik; Park, Y. D.; Mickey, D. L.

doi:10.1086/338891

Cited by 63 publications

(79 citation statements)

References 35 publications

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“…In contrast, Gary et al (1987) found that another analyzed AR was indeed force-free, except for some, localized areas (areas for which flaring activity was noticed). Moon et al (2002) analyzed the forces within three flare-productive ARs and found a median of ≈0.1 for the net vertical Lorentz force and argued that the magnetic field at photospheric levels may not be as far from being force-free as commonly assumed. (See also Sect.…”

Section: Relative Importance Of Magnetic Forcesmentioning

confidence: 99%

The magnetic field in the solar atmosphere

Wiegelmann

Thalmann

Solanki

2014

Astron Astrophys Rev

172

125

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This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes.

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Section: Relative Importance Of Magnetic Forcesmentioning

confidence: 99%

The magnetic field in the solar atmosphere

Wiegelmann

Thalmann

Solanki

2014

Astron Astrophys Rev

172

125

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“…Moon et al (2002), studying the force-free extent in the photosphere using 12 vector magnetograms of three active regions, realised that the photospheric magnetic fields are not very far from the force-free case. Liu et al (2011b) tentatively applied the force-free extrapolation to reconstruct the magnetic fields above the quiet region and checked the force-free extent of this quiet region based on the high spatial resolution vector magnetograms observed by the Solar Optical Telescope/Spectro-Polarimeter on board Hinode.…”

Section: Introductionmentioning

confidence: 99%

A Statistical Study on Force-Freeness of Solar Magnetic Fields in the Photosphere

Liu

Zhang

et al. 2013

Publ. Astron. Soc. Aust.

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It is an indisputable fact that solar magnetic fields are force-free in the corona, where force-free fields mean that current and magnetic fields are parallel and there is no Lorentz force in the fields. While the force-free extent of photospheric magnetic fields remains open, in this paper, we give its statistical results. Vector magnetograms (namely, Bx, By, and Bz in heliocentric coordinates) employed are observed by the Solar Magnetic Field Telescope at Huairou Solar Observing Station. We study and calibrate 925 magnetograms calibrated by two sets of calibration coefficients, which indicate the relation between magnetic fields and the strength of the Stokes spectrum and can be calculated either theoretically or empirically. The statistical results show that the majority of active region magnetic fields are not consistent with the force-free model.

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“…In equilibrium, the coronal magnetic field is nearly force-free in the major part of active regions, except their upper periphery (see, e.g., Metcalf et al 1995;Moon et al 2002;Gary 2001). To a very good approximation it can therefore be described by ∇ × B = αB with ∇ · B = 0.…”

Section: Introductionmentioning

confidence: 99%

Testing magnetofrictional extrapolation with the Titov-Démoulin model of solar active regions

Valori¹,

Kliem

Török³

et al. 2010

A&A

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We examine the nonlinear magnetofrictional extrapolation scheme using the solar active region model by Titov and Démoulin as test field. This model consists of an arched, line-tied current channel held in force-free equilibrium by the potential field of a bipolar flux distribution in the bottom boundary. A modified version with a parabolic current density profile is employed here. We find that the equilibrium is reconstructed with very high accuracy in a representative range of parameter space, using only the vector field in the bottom boundary as input. Structural features formed in the interface between the flux rope and the surrounding arcade -"hyperbolic flux tube" and "bald patch separatrix surface" -are reliably reproduced, as are the flux rope twist and the energy and helicity of the configuration. This demonstrates that force-free fields containing these basic structural elements of solar active regions can be obtained by extrapolation. The influence of the chosen initial condition on the accuracy of reconstruction is also addressed, confirming that the initial field that best matches the external potential field of the model quite naturally leads to the best reconstruction. Extrapolating the magnetogram of a Titov-Démoulin equilibrium in the unstable range of parameter space yields a sequence of two opposing evolutionary phases, which clearly indicate the unstable nature of the configuration: a partial buildup of the flux rope with rising free energy is followed by destruction of the rope, losing most of the free energy.

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Force‐Freeness of Solar Magnetic Fields in the Photosphere

Cited by 63 publications

References 35 publications

The magnetic field in the solar atmosphere

The magnetic field in the solar atmosphere

A Statistical Study on Force-Freeness of Solar Magnetic Fields in the Photosphere

Testing magnetofrictional extrapolation with the Titov-Démoulin model of solar active regions

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