The sun is observed to be a torsional oscillator with a period of 11 years

Twelve years of full-disk Mount Wilson velocity data have been analyzed to study horizontal east-west motions. A torsional wave pattern with alternating latitude zones of slow and fast rotation is found, after subtracting a differentially rotating frame. Amplitudes of the flow pattern average about 3 m/s. It requires about 22 years for zones to drift from the poles, where they originate, to the equator, where they disappear. The pattern is symmetric about the equator. The zones representing the next solar cycle (No. 22) are seen now at high solar latitudes. Solar active regions are formed in a latitude strip centered on the boundary of fast- and slow-velocity zones. This pattern evidently represents a deep-seated circulation pattern and is the first evidence of the association of mass motions with large-scale characteristics of the solar activity cycle.