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Evolution of the Sun's magnetic polarities

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Abstract

The global magnetic-field resonances previously found in a modal analysis of a 25 yr Mt Wilson-Kitt Peak data set of synoptic magnetic maps are also revealed when only the magnetic polarities are used, disregarding the magnitude of the flux. Thus the topological organization of the magnetic polarities alone suffices to bring out the correct modal structure, although the results are noisier as compared with the case when the magnetic fluxes are included.

This result suggests that magnetic polarities indirectly inferred from Hα data may be used to study the resonances. Whereas synoptic magnetograph observations are not available before 1959, Hα observations date back to the last century, and could in principle be used to enhance the frequency resolution in the power spectra.

Using zonal distributions of magnetic polarities inferred from Hα data by Makarov for the period 1941–1983, we have performed a power spectrum analysis of the rotationally symmetric spherical harmonic modes (m = 0), and compared the results with the corresponding analysis for the magnetic fields and polarities determined from real magnetograph data. The same parity selection rule that governs the 22 yr magnetic cycle in the magnetograph data is also revealed by the Hα data. The Hα results are however much noisier and do not show the pattern of resonant frequencies discovered in the magnetograph data for the modes of even parity. It is concluded that only real magnetograph data should be used to investigate the global resonances in the magnetic-field pattern.

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Authors and Affiliations

  1. Institute of Astronomy, ETH-Zentrum, CH-8092, Zürich, Switzerland

    J. O. Stenflo & A. L. Weisenhorn

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  1. J. O. Stenflo
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  2. A. L. Weisenhorn
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Stenflo, J.O., Weisenhorn, A.L. Evolution of the Sun's magnetic polarities. Sol Phys 108, 205–220 (1987). https://doi.org/10.1007/BF00214161

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  • DOI: https://doi.org/10.1007/BF00214161

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