A method of resolving the 180 degree ambiguity by employing the chirality of solar features
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A Method of Resolving the 180-Degree Ambiguity by Employing the Chirality of Solar Features. S. F. Martin, Y. Lin, O. Engvold 2008, Sol. Phys. 250, 31. Abstract. Resolving the 180-degree ambiguity in magnetic field direction of prominence axis with the “chiral method”.

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

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A method of resolving the 180 degree ambiguity by employing the chirality of solar features

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

S. F. Martin, Y. Lin, O. Engvold

2008, Sol. Phys. 250, 31


Abstract

Abstract

  • Resolving the 180-degree ambiguity in magnetic field direction of prominence axis with the “chiral method”.

    • there is a large component of the magnetic field that is parallel with the polarity reversal boundary

  • A second purpose is to illustrate that filaments have a continuous spectrum of properties

    • no difference fundamentally between active-region filaments and quiescent filaments


Filament axis spine

Filament axis (spine)

  • Spine is a magnetic field entirely parallel to the polarity reversal boundary

    • material is flowing along the spine, but not across the spine


What is chirality

What is “chirality” ?

dextral filament

  • Dextral

    • barbs veer away from us to the right when we are on the axis (main body of prominence)

Hαcenter

Hα wing


What is chirality1

What is “chirality” ?

sinistral filament

  • Sinistral

    • barbs veer away from us to the left when we are on the axis (main body of prominence)

Hαcenter

Hα wing


Barbs and minority polarity

Barbs and minority polarity

  • Barbs are:

    • appendages along the sides of a filament that extend from the spine

    • related to patches of minority polarity

dextral

sinistral

Martin (1998)


Chiral method

Chiral method

  • Chirality

    • exists in barbs, fibrils, coronal loops, sigmoids, erupting prominences

    • can be seen in images of medium spatial resolution (1-2”) as well as magnetogram to define the polarity of plage or network

  • Chirality relationships between different solar features (related to the same polarity reversal boundary) have one-to-one correspondences in sign without exception

  • 180-degree ambiguity can be resolved with the majority polarity and the chirality


Example

Example

Dextral

Sinistral


Example 1

Example 1

Dextral

Sinistral

  • Active region

    • The polarity on upper side of the filament is positive.

    • Tiny sinistral barbs on the south side of the filament.

Arrows in the figures indicate magnetic field direction resolved with the chirality method.


Example 2

Example 2

Dextral

Sinistral

  • Border of an active region

    • positive polarity in the active region

    • negative polarity in the network

sinistral


Example 3

Example 3

Dextral

Sinistral

  • Intermediate filament channel and filament

dextral


Example 4

Example 4

Dextral

Sinistral

  • Spine and barbs of a quiescent filament

    • left side shows sinistral

    • right side is dextral ?

    • nearly parallel to the axis

    • quiescent filaments sometimes have barbs that deviate from the filament axis at an angle seemingly prevents the identification of the filament as either sinistral or dextral from the apparent direction of its barbs

dextral ?

sinistral


Example 41

Example 4

Dextral

Sinistral

  • Spine and barbs of a quiescent filament

    • left side shows sinistral with curtain-like structure

      • barbs do not appear anomalous if threads in the curtain contain mass

    • right side also has curtain type of barbs

      • the direction is the same as sinistral

    • invisible barbs ?  sinistral

sinistral

sinistral

Chirality should be determine from the chirality of a majority of the barbs and not from a single apparent barb.


Example 5

Example 5

Dextral

Sinistral

  • Merging or lack of merging of filaments

    • filaments with the same chirality can merge (Schmieder et al. 2004)

    • there are several gaps in Hα, where it appears to be continuous in EIT 304A although the contrast is lower

sinistral


Example 6

Example 6

Dextral

Sinistral

  • Merging or lack of merging of filaments

    • two filaments: AR and QS

    • before 17 Aug., the chirality of an AR filament is not known.

    • but it merges with sinistral quiescent filament.

    • then the AR filament is found out to be sinistral.

    • this insicates that AR and QS filaments are physically the same types of structure.

sinistral


Example 7

Example 7

Dextral

Sinistral

  • Very low magnetic fluxdensity

    • barbs are often nearly perpendicular to the axis

sinistral ?


Example 8

Example 8

Dextral

Sinistral

  • Very low magnetic fluxdensity

    • the chirality is not clearly seen near the limb

    • but, several days before, the chirality is dextral

    • (chirality generally does not change with time)

dextral


Conclusion

Conclusion

  • Complementary method to resolve 180-degree ambiguity with the chiral method, given that adequate solar images are available.

  • There is no fundamental difference between active region and quiescent filaments because they can merge.


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