These features of the Sun's magnetic dynamo can all be seen in a movie of the Sun's magnetic field over the last 30-years (86 Mb AVI Movie).

Magnetic fields are produced by electric currents. These currents are generated within the Sun by the flow of the Sun's hot, ionized gases. We observe a variety of flows on the Sun's surface and within its interior. Nearly all of these flows may contribute in one way or another to the production of the Sun's magnetic field.

Magnetic fields are a little like rubber bands. They consist of continuous loops of lines of force that have both tension and pressure. Like rubber bands, magnetic fields can be strengthened by stretching them, twisting them, and folding them back on themselves. This stretching, twisting, and folding is done by the fluid flows within the Sun.

The Omega Effect

Magnetic fields within the Sun are stretched out and wound around the Sun by differential rotation - the change in rotation rate as a function of latitude and radius within the Sun. This is called the omega-effect after the Greek letter used to represent rotation. The Sun's differential rotation with latitude can take a north-south oriented magnetic field line and wrap it once around the Sun in about 8 months.

The Alpha Effect

Twisting of the magnetic field lines is caused by the effects of the Sun's rotation. This is called the alpha-effect after the Greek letter that looks like a twisted loop. Early models of the Sun's dynamo assumed that the twisting is produced by the effects of the Sun's rotation on very large convective flows that carry heat to the Sun's surface. One problem with this assumption is that the expected twisting is far too much and it produces magnetic cycles that are only a couple years in length.

The Interface Dynamo

Early models of the Sun's magnetic dynamo worked on the idea that the dynamo activity occurs throughout the entire convection zone. It was soon realized, however, that magnetic fields within the convection zone would rapidly rise to the surface and wouldn't have enough time to experience either the alpha or the omega effect. Since a magnetic field exerts a pressure on its surroundings, regions with a magnetic field should push aside the surrounding gas and make a bubble that would continue to rise all the way to the surface.

The Meridional Flow

The Sun's meridional flow - the flow of material along meridian lines from the equator toward the poles at the surface and from the poles to the equator below the surface- must also play an important role in the Sun's magnetic dynamo. At the surface this flow is a slow 20 m/s (40 mph) but the return flow toward the equator inside the Sun where the density is much higher must be much slower still - 1 to 2 m/s (2 to 4 mph). This slow return flow would carry material from the mid-latitudes to the equator in about 11 years.