Shear angle of magnetic fields |
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Authors: | Yanping Lü Jingxiu Wang Huaning Wang |
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Institution: | (1) Beijing Astronomical Observatory, Chinese Academy of Sciences, 100080 Beijing, China |
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Abstract: | In this paper we introduce a new parameter, the shear angle of vector magnetic fields, ![Delta](/content/w0t6235w2k233502/xxlarge916.gif) , to describe the non-potentiality of magnetic fields in active regions, which is defined as the angle between the observed vector magnetic field and its corresponding current-free field. In the case of highly inclined field configurations, this angle is approximately equal to the angular shear , ![Delta](/content/w0t6235w2k233502/xxlarge916.gif) , defined by Hagyardet al. (1984). The angular shear, ![Delta](/content/w0t6235w2k233502/xxlarge916.gif) , can be considered as the projection of the shear angle, ![Delta](/content/w0t6235w2k233502/xxlarge916.gif) , on the photosphere. For the active region studied, the shear angle, ![Delta](/content/w0t6235w2k233502/xxlarge916.gif) , seems to have a better and neater correspondence with flare activity than does ![Delta](/content/w0t6235w2k233502/xxlarge916.gif) . The shear angle, ![Delta](/content/w0t6235w2k233502/xxlarge916.gif) , gives a clearer explanation of the non-potentiality of magnetic fields. It is a better measure of the deviation of the observed magnetic field from a potential field, and is directly related to the magnetic free energy stored in non-potential fields. |
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