An Optimization Approach to Reconstructing Force‐free Fields

Wheatland, M. S.; Sturrock, P. A.; Roumeliotis, G.

doi:10.1086/309355

Cited by 456 publications

(442 citation statements)

References 12 publications

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“…We then correct for projection effects and transform the line-of-sight and transverse components of the vector magnetic field to the heliographic components as described in Gary & Hagyard (1990). Finally, an NLFFF extrapolation is made to obtain the magnetic field configuration with the optimization method (Wheatland et al 2000;Wiegelmann 2004). Figure 3b depicts the magnetic field lines and the 3600 Å contours.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

Understanding the white-light flare on 2012 March 9: evidence of a two-step magnetic reconnection

Hao¹,

Guo²,

Dai³

et al. 2012

A&A

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Aims. We attempt to understand the white-light flare (WLF) that was observed on 2012 March 9 with a newly constructed multiwavelength solar telescope called the Optical and Near-infrared Solar Eruption Tracer (ONSET). Methods. We analyzed WLF observations in radio, Hα, white-light, ultraviolet, and X-ray bands. We also studied the magnetic configuration of the flare via the nonlinear force-free field (NLFFF) extrapolation and the vector magnetic field observed by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). Results. Continuum emission enhancement clearly appeared at the 3600 Å and 4250 Å bands, with peak contrasts of 25% and 12%, respectively. The continuum emission enhancement closely coincided with the impulsive increase in the hard X-ray emission and a microwave type III burst at 03:40 UT. We find that the WLF appeared at one end of either the sheared or twisted field lines or both. There was also a long-lasting phase in the Hα and soft X-ray bands after the white-light emission peak. In particular, a second, yet stronger, peak appeared at 03:56 UT in the microwave band. Conclusions. This event shows clear evidence that the white-light emission was caused by energetic particles bombarding the lower solar atmosphere. A two-step magnetic reconnection scenario is proposed to explain the entire process of flare evolution, i.e., the firststep magnetic reconnection between the field lines that are highly sheared or twisted or both, and the second-step one in the current sheet, which is stretched by the erupting flux rope. The WLF is supposed to be triggered in the first-step magnetic reconnection at a relatively low altitude.

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Section: Data Analysis and Resultsmentioning

confidence: 99%

Understanding the white-light flare on 2012 March 9: evidence of a two-step magnetic reconnection

Hao¹,

Guo²,

Dai³

et al. 2012

A&A

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show abstract

“…However, since magnetic shear on the photosphere is unevenly distributed in general, the extrapolation of the linear force-free field may not be a good assumption of the coronal field. A mathematical formula for constructing the nonlinear forcefree field, in which is a function of flux tube, from vector magnetograph observations has been proposed by a couple of papers (Sakurai 1981;Wheatland, Sturrock, & Roumeliotis 2000;Wang, Yan, & Sakurai 2001). The second method is more straightforwardly applicable to observations.…”

Section: Introductionmentioning

confidence: 99%

Measurement of Magnetic Helicity Injection and Free Energy Loading into the Solar Corona

Kusano

Maeshiro

Yokoyama

et al. 2002

ApJ

223

195

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We develop a new methodology that can determine magnetic helicity flux as well as Poynting flux across the photosphere based on magnetograph observation. By applying this method, we study the injection mechanism of magnetic helicity and magnetic free energy into the solar corona. In order to derive the helicity and energy fluxes, first the velocity tangential to the solar surface is constructed by applying a correlation tracking technique on the magnetic observation, and second, the velocity component normal to the photosphere is derived from the condition that the magnetic evolution must be consistent with the induction equation. Through this procedure, we can determine the helicity and energy fluxes separately for the shear motion effect and for the flux emergence effect. Based on this new method, NOAA Active Region 8100 was analyzed from 1997 November 1 to 5 using data observed by the Solar and Heliospheric Observatory Michelson Doppler Interferometer and the vector magnetograph at the National Astronomical Observatory of Japan (NAOJ) in Tokyo. The results indicate that the photospheric shear motion and the flux emergence process have equally contributed to the helicity injection and have supplied magnetic helicity of opposite signs into this active region.

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“…The preprocessed bottom boundary are used by the optimization code to extrapolate the NLFFF (Wheatland et al 2000;Wiegelmann 2004). Selected field lines are plotted in Figure 1.…”

Section: Analysis and Resultsmentioning

confidence: 99%

A filament supported by different magnetic field configurations

et al. 2010

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Abstract.A nonlinear force-free magnetic field extrapolation of vector magnetogram data obtained by THEMIS/MTR on 2005 May 27 suggests the simultaneous existence of different magnetic configurations within one active region filament: one part of the filament is supported by field line dips within a flux rope, while the other part is located in dips within an arcade structure. Although the axial field chirality (dextral) and the magnetic helicity (negative) are the same along the whole filament, the chiralities of the filament barbs at different sections are opposite, i.e., right-bearing in the flux rope part and left-bearing in the arcade part. This argues against past suggestions that different barb chiralities imply different signs of helicity of the underlying magnetic field. This new finding about the chirality of filaments will be useful to associate eruptive filaments and magnetic cloud using the helicity parameter in the Space Weather Science.

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An Optimization Approach to Reconstructing Force‐free Fields

Cited by 456 publications

References 12 publications

Understanding the white-light flare on 2012 March 9: evidence of a two-step magnetic reconnection

Understanding the white-light flare on 2012 March 9: evidence of a two-step magnetic reconnection

Measurement of Magnetic Helicity Injection and Free Energy Loading into the Solar Corona

A filament supported by different magnetic field configurations

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