The Solar Dynamo

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Magnetic fields and charged particles go hand in hand.

• Magnetic fields are produced by the motions of charged particles
• Charged particles are accelerated by magnetic fields:

Because of this force, charged particles cannot cross magnetic field lines. Or depending on your point of view, magnetic field lines are unable to move freely through a sea of charged particles. We say that the magnetic field lines are frozen in.

• Remember the convective motions in the Sun? These are moving charged particles, and set up a strong magnetic field. Initially the magnetic field would be a dipole, like a magnet:

• But the Sun rotates differentially, right? The poles rotate slower than the equator. This differential rotation causes the magnetic field of the Sun to wind up.

• As the magnetic field lines wind up and become a toroidal field, they can form kinks which break through the surface.

• Where they break through the surface, they inhibit convection cells underneath them from rising to the surface. Remember, charged particles cannot cross magnetic field lines! Since there is no hot gas rising, so the surface stays cooler: sunspots! Sunspots occur in pairs, where the field line first breaks out of the Sun, then where it goes back in.

• This continues, first near the poles, then closer to the equator, until the magnetic field lines are so tightly would up that magnetic reconnection reestablishes the simple dipole field, but with the polarity reversed. Then it all starts again...