Solar dynamo

The solar dynamo is the physical process that generates the Sun's magnetic field. A dynamo, essentially a naturally occurring electric generator in the Sun's interior, produces electric currents and a magnetic field, following the laws of Ampère, Faraday and Ohm, as well as the laws of hydrodynamics, which together form the laws of magnetohydrodynamics. The detailed mechanism of the solar dynamo is not known and is the subject of current research.

A dynamo converts kinetic energy into electric-magnetic energy. An electrically conducting fluid with shear or more complicated motion, such as turbulence, can temporarily amplify a magnetic field through Lenz's law: fluid motion relative to a magnetic field induces electric currents in the fluid that distort the initial field. If the fluid motion is sufficiently complicated, it can sustain its own magnetic field, with adjective fluid amplification essentially balancing diffusive or ohmic decay. Such systems are called self-sustaining dynamos. The Sun is a self-sustaining dynamo that converts convective motion and differential rotation within the Sun to electric-magnetic energy.

The most prominent time variation of the solar magnetic field is related to the quasi-periodic 11-year solar cycle, characterized by an increasing and decreasing number and size of sunspots. Sunspots are visible as dark patches on the Sun's photosphere and correspond to concentrations of magnetic field. At a typical solar minimum, few or no sunspots are visible. Those that do appear are at high solar latitudes. As the solar cycle progresses towards its maximum, sunspots tend to form closer to the solar equator, following Spörer's law.

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