The magnetic-field geometry in polar ray structures of the solar corona

Filippov, B. P.; Platov, Yu. V.; Ajabshirizadeh, A.; Klepikov, D. V.

doi:10.1134/1.1800178

Cited by 3 publications

(1 citation statement)

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“…The deep location of the focuses near activity maximum could be explained by complicated relationship between the harmonics of a "new" cycle and an "old" cycle during the process of polarity reversal. The expression for q for the sum of two harmonics is given by (Filippov, Platov & Klepikov 2004) …”

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Polar magnetic field geometry in the solar cycle and the relationship between spherical harmonics

2004

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Abstract. Geometry of the polar magnetic field is changing during the activity cycle. Tangents to polar ray structures are usually crossed near some point below the surface. This point can be named as a "magnetic focus". The distance q between the focus and the center of the solar disk changes from the maximum value about 0.7 R at solar minimum activity to the minimum value about 0.5 R at solar maximum. This behavior has not been understood till now. Really, all tangents to field lines near the pole of the axially symmetric potential magnetic field described by zonal spherical harmonics cross at the same point. However, the greater is the number of a harmonic, the closer to the surface is the crossing point. As far as at activity maximum high harmonics dominate, the behavior of the focuses seems to be in contradiction with the results of the harmonic analysis. We have found that the focus depth changes could be explained by complicated relationship between the harmonics of "new" and "old" cycle near the instant of the polar magnetic field reversal.

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Polar magnetic field geometry in the solar cycle and the relationship between spherical harmonics

2004

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Polar Coronal Structures and the Global Magnetic Field Evolution Through the Cycle

et al. 2004

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We compare the shape and position of some plasma formations visible in the polar corona with the cyclic evolution of the global magnetic field. The first type of object is polar crown prominences. A two-fold decrease of the height of polar crown prominences was found during their poleward migration from the middle latitudes to the poles before a polar magnetic field reversal. The effect could be assigned to a decrease of the magnetic field scale. The second type of object is the polar plumes, ray like structures that follow magnetic field lines. Tangents to polar ray structures are usually crossed near some point, "a magnetic focus," below the surface. The distance q between the focus and the center of the solar disk changes from the maximum value about 0.65R at solar minimum activity to the minimum value about 0.45R at solar maximum. At first glance this behaviour seems to be contrary to the dynamics of spherical harmonics of the global magnetic field throughout a cycle. We believe that the problem could be resolved if one takes into account not only scale changes in the global magnetic field but also the phase difference in the cyclic variations of large-scale and small-scale components of the global field.

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