Has anyone figured out why there seems to be an 11 year activity cycle for sunspots?
It is basically because the sun rotaion. It is kind of wierd the central or “equatorial” region of the sun rotates faster than at higher latitudes. So the equator rotates every 25 days and approximately 30 days for polar regions. The rotation is also affected by depth. The interior rotates slower than the equator and it is this differential rotation that causes the sun spot cycle. Which is 22 years, every 11 years the magnetic field is reversed so a full magnetic cycle is 22 years.
This site has a good picture of the ‘Babcock model’ and explains in a lot more detail than I have time for a the moment.
NPR’s Talk of the Nation Science Friday Nov. 14, 2003 had a big segment about solar storm, the sun’s rotation, the 11-year cycle, and such. Here’s a link, I think. http://www.npr.org/rundowns/rundown.php?prgId=5&prgDate=current
Cool stuff.