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AN OVERVIEW OF EXISTING ALGORITHMS FOR RESOLVING THE 180-DEGREE AMBIGUITY IN VECTOR MAGNETIC FIELDS: QUANTITATIVE TESTS WITH SYNTHETIC DATA  

Thomas Metcalf   Submitted: 2006-06-01 10:12

We report here on the present state-of-the-art in algorithms used for resolving the 180circ 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.

Authors: Metcalf, Leka, Barnes, Lites, Georgoulis, Pevtsov, Gary, Jing, Balasubramaniam, Li, Liu, Wang, Abramenko, Yurchyshyn, Moon
Projects: None

Publication Status: Solar Physics, In Press
Last Modified: 2006-06-01 20:43
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Magnetic Free Energy in AR10486 on October 29, 2003  

Thomas Metcalf   Submitted: 2005-03-01 13:13

We calculate the total and the free magnetic energy for solar active region 10486 on 29 Oct 2003 using chromospheric vector magnetograms observed with the Imaging Vector Magnetograph at Mees Solar Observatory in the ion{Na}{1} 5896AA spectral line. The magnetic energy is derived from the magnetic virial theorem using observations spanning the X10 flare that occurred at 20:39 UT. Though poor atmospheric seeing prevented us from discerning changes in the free energy associated with the flare, there was an unusually large amount of free magnetic energy in AR10486: (5.7pm1.9) imes 1033 ergs, which is consistent with the very high level of activity observed in this active region. It is thus plausible that the extreme activity was powered by the magnetic free energy.

Authors: Thomas R. Metcalf, K. D. Leka, and D. L. Mickey
Projects: RHESSI

Publication Status: ApJL in press
Last Modified: 2005-03-01 13:15
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TRACE and YOHKOH Observations of a White Light Flare  

Thomas Metcalf   Submitted: 2003-06-02 11:19

We present observations of a large solar white light flare observed on 2001 Aug 25 using data from the the TRACE white light channel and Yohkoh/HXT. These emissions are consistent with the classic Type I white light flare mechanism and we find that the enhanced white light emission observed by TRACE originates in the chromosphere and temperature minimum regions via non-equilibrium hydrogen ionization induced by direct collisions with the electron beam and by backwarming of the lower atmosphere. The three flare kernels observed in hard X-rays and white light are spatially associated with magnetic separatrices and one of the kernels is observed to move along a magnetic separatrix at 400 km s-1. This is evidence in favor of particle acceleration models which energize the electrons via magnetic reconnection at magnetic separators.

Authors: Metcalf, Alexander, Hudson, and Longcope
Projects: Soho-MDI,Yohkoh-HXT,Yohkoh-SXT

Publication Status: ApJ in press
Last Modified: 2003-06-02 11:19
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Abstracts by Author
AN OVERVIEW OF EXISTING ALGORITHMS FOR RESOLVING THE 180-DEGREE AMBIGUITY IN VECTOR MAGNETIC FIELDS: QUANTITATIVE TESTS WITH SYNTHETIC DATA
Magnetic Free Energy in AR10486 on October 29, 2003
TRACE and YOHKOH Observations of a White Light Flare

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