An Overview of Existing Algorithms for Resolving the 180° Ambiguity in Vector Magnetic Fields: Quantitative Tests with Synthetic Data |
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| Authors: | Thomas R Metcalf K D Leka Graham Barnes Bruce W Lites Manolis K Georgoulis A A Pevtsov K S Balasubramaniam G Allen Gary Ju Jing Jing Li Y Liu H N Wang Valentyna Abramenko Vasyl Yurchyshyn Y-J Moon |
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| Institution: | (1) Northwest Research Associates, Colorado Research Associates Division, 3380 Mitchell Ln., Boulder, CO, 80301, U.S.A.;(2) High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO, 80307-3000, U.S.A.;(3) The Johns Hopkins University, Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD, 20723-6099, U.S.A.;(4) National Solar Observatory, Sunspot, NM, 88349, U.S.A.;(5) NASA/MSFC/NSSTC, Marshall Space Flight Center, Huntsville, AL, 35812, U.S.A.;(6) New Jersey Institute of Technology, Center for Solar-Terrestrial Research, 323 Martin Luther King Boulevard, Newark, NJ, 07102, U.S.A.;(7) Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI, 96822, U.S.A.;(8) Stanford University, HEPL Annex, B210, Stanford, CA, 94305-4085, U.S.A.;(9) National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Rd., Chaoyang District, Beijing, 100012, China;(10) Big Bear Solar Observatory, New Jersey Institute of Technology, 40386 North Shore Lane, Big Bear City, CA, 92314-9672, U.S.A.;(11) Korea Astronomy and Space Science Institute, 61-1 Hwaam-dong, Yuseong-gu, Daejeon, 305-348, South Korea |
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| 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. |
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