A Method of Resolving the 180-Degree Ambiguity by Employing the Chirality of Solar Features

Abstract

The 180-degree ambiguity in magnetic field direction along polarity reversal boundaries can be resolved often and reliably by the chiral method. The chiral method requires (1) identification of the chirality of at least one solar feature related to a polarity reversal boundary along which the field direction is sought and (2) knowledge of the polarity of the network magnetic field on at least one side of the polarity reversal boundary. In the context of the Sun, chirality is an observable signature of the handedness of the magnetic field of a solar feature. We concentrate on how to determine magnetic field direction from chirality definitions and illustrate the technique in eight examples. The examples cover the spectrum of polarity boundaries associated with filament channels and filaments ranging from those connected with active regions to those on the quiet Sun. The applicability of the chiral method to all categories of filaments supports the view that active region filaments and quiescent filaments are the extreme ends in a continuous spectrum of filaments.The chiral method is almost universally applicable because many types of solar features that reveal chirality are now readily seen in solar images accessible over the World Wide Web; also there are clear differences between left-handed and right-handed solar structures that can be identified in both high-and low-resolution data although high-resolution images are almost always preferable. In addition to filaments and filament channels, chirality is identifiable in coronal loop systems, flare loop systems, sigmoids, some sunspots, and some erupting prominences. Features other than filament channels and filaments can be used to resolve the 180-degree ambiguity because there is a one-to-one relationship between the chiralities of all features associated with a given polarity reversal boundary.Y. Lin is now at

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

“…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.…”

Physics of Solar Prominences: II—Magnetic Structure and Dynamics

“…In general due to the lack of high resolution Hα data and direct measurements of magnetic fields within prominences, filaments are mostly classified using their relationship to barbs (Pevtsov et al, 2003;Yeates et al, 2007). López and Martin et al (2008) used the chirality rules to resolve the 180-degree ambiguity in photospheric vector-field measurements. In force-free field models (e.g., Mackay, Longbottom & Priest, 1999;Mackay and van Ballegooijen, 2005) this chirality is directly related to the dominant sign of magnetic helicity that is contained within the filament and filament channel.…”

Damping of Fast Magnetohydrodynamic Oscillations in Quiescent Filament Threads

“…The measured average width of resolved threads is about 0.3Љ (∼210 km), whereas the length is between 5Љ and 40Љ (∼3500-28,000 km). They seem to be partially filled with cold plasma (Lin et al 2005), typically 2 orders of magnitude denser than that of the corona, and it is generally assumed that they outline their magnetic flux tubes (Engvold 1998;Lin 2004;Lin et al 2005;Martin et al 2008). This idea is strongly supported by the fact that they are inclined with respect to the filament-long axis at a similar angle to what has been found for the magnetic field (Leroy 1980;Bommier et al 1994;Bommier & Leroy 1998).…”