Journal ArticleDOI
An Overview of Existing Algorithms for Resolving the 180° Ambiguity in Vector Magnetic Fields: Quantitative Tests with Synthetic Data
Thomas R. Metcalf,K. D. Leka,Graham Barnes,Bruce W. Lites,Manolis K. Georgoulis,Alexei A. Pevtsov,Krishnan Balasubramaniam,G. Allen Gary,Ju Jing,Jing Li,Yang Liu,Huaning Wang,Valentyna Abramenko,Vasyl Yurchyshyn,Yong-Jae Moon +14 more
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TLDR
In this article, the authors report on the state-of-the-art in algorithms used for resolving the 180° ambiguity in solar vector magnetic field measurements and compare them quantitatively and seek to understand where each succeeds, where it fails and why.Abstract:
We report here on the present state-of-the-art in algorithms used for resolving the 180° ambiguity in solar vector magnetic field measurements. With present observations and techniques, some assumption must be made about the solar magnetic field in order to resolve this ambiguity. Our focus is the application of numerous existing algorithms to test data for which the correct answer is known. In this context, we compare the algorithms quantitatively and seek to understand where each succeeds, where it fails, and why. We have considered five basic approaches: comparing the observed field to a reference field or direction, minimizing the vertical gradient of the magnetic pressure, minimizing the vertical current density, minimizing some approximation to the total current density, and minimizing some approximation to the field's divergence. Of the automated methods requiring no human intervention, those which minimize the square of the vertical current density in conjunction with an approximation for the vanishing divergence of the magnetic field show the most promise.read more
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Journal ArticleDOI
Alfv\'en Wave Dissipation in the Solar Chromosphere
S. D. T. Grant,David B. Jess,Teimuraz V. Zaqarashvili,C. Beck,Hector Socas-Navarro,Markus J. Aschwanden,P. H. Keys,Damian J. Christian,S. J. Houston,Rebecca L. Hewitt +9 more
TL;DR: In this article, the authors provided the first observational evidence of magneto-hydrodynamic (MHD) Alfven waves heating chromospheric plasma in a sunspot umbra through the formation of shock fronts.
Journal ArticleDOI
Radio Emissions from Solar Active Regions
TL;DR: In this article, a review of the efforts to understand these radiative processes, and use them as diagnostic tools to address a number of critical issues involved with active regions is presented.
Journal ArticleDOI
Successive X-class flares and coronal mass ejections driven by shearing motion and sunspot rotation in active region NOAA 12673
TL;DR: In this article, a case study on the occurrence of two successive X-class flares including a decade-class flare (X9.3) and two coronal mass ejections (CMEs) triggered by shearing motion and sunspot rotation in active region NOAA 12673 on 2017 September 6.
Journal ArticleDOI
Validation and Benchmarking of a Practical Free Magnetic Energy and Relative Magnetic Helicity Budget Calculation in Solar Magnetic Structures
TL;DR: In this paper, a nonlinear force-free (NLFF) method is proposed to self-consistently calculate the coronal free magnetic energy and the relative magnetic helicity budgets of observed solar magnetic structures.
Journal ArticleDOI
Measurements of Photospheric and Chromospheric Magnetic Fields
TL;DR: In this article, the authors present an overview of magnetic field measurements in the solar photosphere and highlight some promising future developments for their solution, and discuss the problems of determining magnetic fields at smallest spatial scales with increasing demands on polarimetric sensitivity and temporal resolution.
References
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Book ChapterDOI
The Solar Oscillations Investigation — Michelson Doppler Imager
Philip H. Scherrer,R. S. Bogart,R. I. Bush,J. T. Hoeksema,Alexander G. Kosovichev,Jesper Schou,W. Rosenberg,L. Springer,T. D. Tarbell,A. M. Title,C. J. Wolfson,I. Zayer +11 more
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