Study of Sun’s ‘Hydromagnetic’ Oscillations Using Sunspot Data

Abstract

Spherical- harmonic-fourier CSHF) 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 interf erence 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 _≳9°. The amplitudes and phases do 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 a ℓ ³ exp (-bℓ) expected for waves trapped between the poles.