Global modes constituting the solar magnetic cycle |
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| Authors: | M H Gokhale J Javaraiah |
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| Institution: | (1) Indian Institute of Astrophysics, 560 034 Bangalore, India |
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| Abstract: | We show that the axisymmetric odd degree SHF modes of 21.4-yr periodicity and degrees l  29 in the solar magnetic field (as inferred from sunspot data during 1874–1976), are at least approximately stationary. Among the sine and cosine components of these SHF modes we find four groups, each defining the geometry of a coherent global oscillation characterized by a distinct power hump and its own level of variation. The first two of these  geometrical eigenmodes (viz., B
1 and B
2), define the large-scale structure of the butterfly diagrams. Remaining SHF modes define the orderliness of the field distribution even within the wings of the butterflies down to scales l  29. These include the geometrical eigenmodes B
3 and B
4, which are not present in simulated data sets in which the latitudes of the sunspot groups are randomly redistributed within the wings of the butterflies.Superposition of B
1, B
2, B
3, and B
4 is necessary and sufficient to reproduce important observed properties of the latitude-time distribution of the real field, not only in the sunspot zone, but also in the middle (35°–75°) and the high ( 75°) latitudes, with appropriate relative orders of magnitude and phases. Thus, B
1, B
2, B
3, and B
4 seem to represent really existing global oscillations in the Sun's internal magnetic field. The geometrical form of B
1 may also be the form of the forcing oscillation. |
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