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

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 the Institute of Theoretical Astrophysics, University of Oslo.