Sunspot activity as originating in interference of the Sun's global MHD oscillations

Spherical-harmonic-Fourier analysis of sunspot activity during 1902-54 shows that the sunspot occurrence probability is given by superposition of, mainly, axisymmetric even degree SHF modes of l≤22, all having periods ∼11 yr. The amplitudes and the phases of these modes are found to remain approximately constant over the five cycles, but the small variations in the phases seem to be systematic and coherent. The combination of the amplitudes and the phases determined is unique in reproducing the main qualities of the butterfly diagrams. (author)