An Overview of Existing Algorithms for Resolving the 180° Ambiguity in Vector Magnetic Fields: Quantitative Tests with Synthetic Data

Metcalf, Thomas R.; Leka, K. D.; Barnes, G.; Lites, B. W.; Georgoulis, Manolis K.; Pevtsov, Alexei A.; Balasubramaniam, Krishnan; Gary, G. A.; Jing, Ju; Li, Jing; Liu, Y.; Wang, H. N.; Abramenko, V. I.; Yurchyshyn, Vasyl; Moon, Yong‐Jae

doi:10.1007/s11207-006-0170-x

Cited by 273 publications

(284 citation statements)

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“…To do the physical analyses for the solar eruptive events, a higher-resolution grid should be used in the NLFFF extrapolation calculations (e.g., 1″/pixel, the same resolution as the XRT images). For the magnetograms that are not at the central area of the Sun's disk, the projection effect and the 180°ambiguity in the SP magnetic field data also need to be resolved more carefully and accurately [Georgoulis, 2005;Metcalf et al, 2006;Wiegelmann et al, 2008;Martin et al, 2008;Leka et al, 2009]. Besides the comparison between the extrapolated field lines and the coronal loop images, and the preliminary physical analyses used in this paper, topological techniques and more physical measures should be introduced to quantitatively analyze the topological and physical properties of the extrapolated fields [Longcope, 2005;Zhao et al, 2005;DeVore and Antiochos, 2000;Bleybel et al, 2002;Zhang and Low, 2005;Régnier and Canfield, 2006;Démoulin, 2007;Thalmann et al, 2008;Schrijver et al, 2008;DeRosa et al, 2009] and their relationships to the solar eruptive events.…”

Section: Discussionmentioning

confidence: 99%

“…[29] The 180°ambiguity in the Level 2 data of the three SP vector magnetograms was resolved by using the method proposed by Wang et al [2001], in which the azimuth of the magnetic field is determined by a reference field (LFFF) with a force-free factor best fitting the observed field [Wang et al, 2001;Metcalf et al, 2006]. In order to apply the azimuth disambiguation algorithm, the original SP magnetogram data (nonuniform 1000 × 512 grid, hereinafter referred to as original data) were first resampled to a uniform grid with 582 × 320 pixels (0.507″/pixel, hereinafter referred to as resampled data).…”

Section: Sot-sp Photospheric Vector Magnetogramsmentioning

confidence: 99%

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Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

Wang

Yan

2011

J. Geophys. Res.

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[1] The Hinode satellite can obtain high-quality photospheric vector magnetograms of solar active regions and the simultaneous coronal loop images in soft X-ray and extreme ultraviolet (EUV) bands. In this paper, we continue the work of and apply the newly developed upward boundary integration computational scheme for the nonlinear force-free field (NLFFF) extrapolation of the coronal magnetic field to the

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Section: Discussionmentioning

confidence: 99%

Section: Sot-sp Photospheric Vector Magnetogramsmentioning

confidence: 99%

Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

Wang

Yan

2011

J. Geophys. Res.

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“…A plethora of methods have been proposed to resolve this ambiguity (for an overview, see Metcalf et al, 2006). For disambiguation of HMI data, a variant on the "Minimum Energy" method (Metcalf, 1994) called ME0 has been implemented.…”

Section: The Disambiguation Algorithmmentioning

confidence: 99%

“…This method has been shown to be among the best performing on a wide range of tests on synthetic data for which the answer is known (Metcalf et al, 2006;Leka et al, 2009). However, Leka et al (2009) showed that the minimum energy state is not always the correct ambiguity resolution in the presence of noise.…”

Section: The Disambiguation Algorithmmentioning

confidence: 99%

“…A neighboring-pixel acute-angle algorithm based on the University of Hawai'i Iterative method (UHIM; Canfield et al, 1993;Metcalf et al, 2006) that locally maximizes the sum of the dot product of the field at one pixel with the field at its neighbors is used. In areas close to pixels with well-determined fields, the method performs well, as it quickly produces a smooth transition to noisy pixels.…”

Section: Treatment Of Areas Dominated By Noisementioning

confidence: 99%

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The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance

et al. 2014

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The Helioseismic and Magnetic Imager (HMI) began near-continuous full-disk solar measurements on 1 May 2010 from the Solar Dynamics Observatory (SDO). An automated processing pipeline keeps pace with observations to produce observable quantities, including the photospheric vector magnetic field, from sequences of filtergrams. The basic vector-field frame list cadence is 135 seconds, but to reduce noise the filtergrams are combined to derive data products every 720 seconds. The primary 720 s observables were released in mid-2010, including Stokes polarization parameters measured at six wavelengths, as well as intensity, Doppler velocity, and the line-of-sight magnetic field. More advanced products, including the full vector magnetic field, are now available. Automatically identified HMI Active Region Patches (HARPs) track the location and shape of magnetic regions throughout their lifetime.The vector field is computed using the Very Fast Inversion of the Stokes Vector (VFISV) code optimized for the HMI pipeline; the remaining 180 • azimuth ambiguity is resolved with the Minimum Energy (ME0) code. The Milne-Eddington inversion is performed on all full-disk HMI observations. The disambiguation, until recently run only on HARP regions, is now implemented for the full disk. Vector and scalar quantities in the patches are used to derive active region indices potentially useful for forecasting; the data maps and indices are collected in the SHARP data series, hmi.sharp_720s. Definitive SHARP processing is completed only after the region rotates off the visible disk; quick-look products are produced in near real time. Patches are provided in both CCD and heliographic coordinates.HMI provides continuous coverage of the vector field, but has modest spatial, spectral, and temporal resolution. Coupled with limitations of the analysis and interpretation techniques, effects of the orbital velocity, and instrument performance, the resulting measurements have a certain dynamic range and sensitivity and are subject to systematic errors and uncertainties that are characterized in this report.

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Variations of the 3‐D coronal magnetic field associated with the X3.4‐class solar flare event of AR 10930

Wang

Yan

et al. 2014

JGR Space Physics

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The variations of the 3-D coronal magnetic fields associated with the X3.4-class flare of active region 10930 are studied in this paper. The coronal magnetic field data are reconstructed from the photospheric vector magnetograms obtained by the Hinode satellite and using the nonlinear force-free field extrapolation method developed in our previous work (He et al., 2011). The 3-D force-free factor , 3-D current density, and 3-D magnetic energy density are employed to analyze the coronal data. The distributions of and current density reveal a prominent magnetic connectivity with strong negative values and strong current density before the flare. This magnetic connectivity extends along the main polarity inversion line and is found to be totally broken after the flare. The distribution variation of magnetic energy density reveals the redistribution of magnetic energy before and after the flare. In the lower space of the modeling volume the increase of magnetic energy dominates, and in the higher space the decrease of energy dominates. The comparison with the flare onset imaging observation exhibits that the breaking site of the magnetic connectivity and site with the highest values of energy density increase coincide with the location of flare initial eruption. We conclude that a cramped positive region appearing in the photosphere causes the breaking of the magnetic connectivity. A scenario for flare initial eruption is proposed in which the Lorentz force acting on the isolated electric current at the magnetic connectivity breaking site lifts the associated plasmas and causes the initial ejection.

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An Overview of Existing Algorithms for Resolving the 180° Ambiguity in Vector Magnetic Fields: Quantitative Tests with Synthetic Data

Cited by 273 publications

References 31 publications

Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance

Variations of the 3‐D coronal magnetic field associated with the X3.4‐class solar flare event of AR 10930

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