Progressive dipole waves as the constituents of the 22-year magnetic cycle

Abstract

A pair of dipole waves propagating with constant phase velocity forward and backward relative to the solar rotation is suggested to explain the characteristic features of the field variation of the 22-year cycles. The interference of these waves results in a single dipole moving with varying phase velocity over the photosphere. The heliographic coordinates of the dipole axis are derived from the harmonic coefficients published for the Mount Wilson observational period 1959–1973. It is found that the dipole axis moves very slowly near the equator at the time of sunspot maximum whereas during the minimum it changes by 180° along a great circle in the direction of the rotation. During minimum the angular velocity of the axis is about ten times larger than during maximum and the poleward elongation of the axis is about 50°.