Study of Sun's "hydromagnetic" Oscillations Using Sunspot Data

Abstract

Spherical-harmonic-fourier (SHF) analysis of sun’s ‘nominal toroidal magnetic field’, computed using sunspot data during 1874-1976, shows that sunspot activity can be considered as possibly originating in interference of sun’s axi-symmetric hydromagnetic’ oscillations of odd degrees up to l ≈ 21 and periods ≈ 22y. The relative amplitudes and relative phases of these oscillations remain fairly constant, leading to butterfly diagrams with stable latitude –time correlations on all latitude scales >9degree the amplitudes and the phases however undergo slow coherent variations. The main modes (l<11) represent an approximately standing oscillation. The mean power spectrum can be fitted excellently to the form al exp (-bl) expected for waves trapped between the poles.