Sunspots were first seen by Galileo, and in the eighteenth century Rudolf Wolf concluded from his study of previous observations that there was a roughly eleven-year solar cycle of activity. In 1919 the astronomer George Ellery Hale found a new solar periodicity, the twenty-two year solar magnetic cycle which is composed of two eleven-year cycles and today is referred to as the Hale cycle. The eleven-year cycle is a complex dynamo process in which the sun’s twisted magnetic fields flip to the opposite direction as the result of the combinatin of the sun’s differential rotation and the convection in its atmosphere. Then, after a second cycle, the original polarity is recovered.
Source:
https://phys.org/news/2021-01-coronal-holes-solar-maximum.html