The Sun exhibits a periodic cycle for solar activity as manifested by solar activity (e.g. sunspots, solar flares). This activity is related to magnetic fields which emerge from the interior of the Sun. The magnetic fields are created by the solar dynamo. The Earth has a dynamo as well but the Earth's magnetic field is (mostly) constant in time. What is some current theories (assuming there isn't one already accepted) that explains for why the solar dynamo generates magnetic fields periodically?