A diagnostic method for probing the possible twist of magnetic field lines in sunspots |
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| Authors: | Shi-Hui Ye Jie-Hai Jin |
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| Institution: | (1) Division of Solar Physics, Purple Mountain Observatory, Academia Sinica, Nanjing, China |
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| Abstract: | In order to study the three-dimensional structure of sunspot magnetic fields it is necessary to determine whether the field lines are twisted, i.e., if the azimuthal angle of transverse field changes with depth. For this purpose we propose the following method. At a fixed point in a spot, and in a certain wavelength interval of a magnetic-sensitive spectral line, one may measure the two Stokes parameters Q and U and then calculate the azimuthal angle of the polarization plane. If the wavelength interval of observation is moved successively from the line center to a wing, one may draw the azimuth diagram by the method proposed by Makita (1986) and refined by us (Ye Shi-hui and Jin Jie-hai, 1987). According to our theoretical calculations, described in this paper, if sunspot field lines are sufficiently strongly twisted, the curve on this diagram contains loop structures. If the twist is rather weak, the curve is approximately semi-circular. From the direction in which the curve winds (clockwise or counterclockwise) one may infer whether the magnetic field is twisting in one direction or in the opposite. In the case of no twist at all, the curve is comparatively simple and similar to a parabola.When the sensitivity of observational data is high enough, our method can also be applied to regions of weak magnetic fields outside sunspots.This work has been supported by the National Natural Science Foundation of China under grant No. 9187006-01. |
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