I thank Bill Abbett, Vasilis Archontis, Sacha Brun, Mark Cheung, Arnab Rai Choudhuri, Laurene Jouve, Evy Kersalé, Alexander Kosovichev, Dana Longcope, Tetsuya Magara, Dibyendu Nandy, Alexei Pevtsov, Matthias Rempel, Manfred Schüssler, and Geoffrey Vasil for permission to include their figures in this article. I also thank Matthias Rempel, Fernando Moreno-Insertis, the scientific editor Manfred Schüssler, and other anonymous referees for reviewing the article (and its updates) and for critical comments that help to improve the article. The National Center for Atmospheric Research is sponsored by the National Science Foundation. This work is also supported by the NASA Heliophysics Guest Investigator Grant NNG07EK66I, and the NASA SDO Science Center Grant NNH09AK02I.
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