ScienceDaily -- Approximately every 11 years the magnetic field on the sun reverses completely -- the north magnetic pole switches to south, and vice versa. It's as if a bar magnet slowly lost its magnetic field and regained it in the opposite direction, so the positive side becomes the negative side. But, of course, the sun is not a simple bar magnet and the causes of the switch, not to mention the complex tracery of moving magnetic fields throughout the eleven-year cycle, are not easy to map out.
MORE: http://www.sciencedaily.com/releases/2012/04/120421203959.htm
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