The Solar Cycle

picture modified from src: SOHO

    Due to the differential rotation, the magnetic field lines eventually tangles and untangles. However, after the untangling of the magnetic field lines, how will the sunspots move?

    No longer linked by the magnetic field lines, the leading spots on each hemisphere will move towards the equator and the following spots will move towards the poles on the respective hemispheres. At the Equator, the leading spots of different polarity will cancel out each other. For the North hemisphere, the following spots with south magnetic polarity will move towards the North Pole; at the South hemisphere, the following spots with north magnetic polarity will travel towards the South Pole. (Like poles repel, unlike poles attract..)

    The following spots with opposite polarity (with respect to the hemisphere) will converge on the Poles. They will first cancel out and then reverse the Sun's overall magnetic field. Guess what, the Sun's Poles is now reversed! The original North Pole is now the South Pole and the original South Pole is now the North Pole! This whole process of "reversing" the poles take 11 years to complete. The solar cycle measures the time taken to reverse the poles and switch back to their original positions. The whole cycle takes 22 years, and for an obvious reason too! For the Poles to revert back to their original positions, you'll need two sunspot cycles. 2 x 11 years = 22 years!!

Resource books: "Universe (Fifth Edition)", "Guide to the Sun"   
Picture of SOHO   

Page of GEM1506K, Group 2 (