Solar dynamo

The Sun is made largely of hot, ionized gas, or plasma. Because plasma conducts electricity, its motion can generate electric currents and magnetic fields. In a stellar dynamo, flows of this conducting fluid continually act on magnetic fields, helping maintain them against resistive decay. Solar physicists infer that much of this process occurs beneath the visible surface, particularly in and around the convection zone, where energy is transported by moving plasma.

The Sun rotates at different rates at different latitudes and depths, a pattern called differential rotation. This shears and winds magnetic field lines, strengthening and transforming parts of the large-scale field. Convection and rotational effects can twist and reorganize the field, while meridional circulation—large-scale flow from the equator toward the poles near the surface, with a return flow deeper inside—transports magnetic flux. Together these processes are central to many explanations of the solar cycle. Models differ over the relative importance and detailed operation of the mechanisms that regenerate the field, especially the poloidal component, whose field lines run roughly from pole to pole.

The familiar sunspot cycle averages about 11 years: sunspots and other signs of magnetic activity increase and decline, and the Sun's polar magnetic fields reverse polarity around the active part of the cycle. A reversal is a regular reorganization of the global magnetic field, not the disappearance of magnetism throughout the Sun. Because the polarity changes after roughly one sunspot cycle, a complete magnetic cycle—return to the original polarity—takes about 22 years. Actual cycles vary, and the timing of changes in the two hemispheres need not be identical.

The broad connection between internal plasma motions and the solar magnetic cycle is well established, but the dynamo is not a fully settled, single-mechanism explanation. Researchers continue to test how differential rotation, turbulent convection, meridional flows, magnetic-field emergence and turbulent transport interact, and where within the Sun each process matters most. Competing models can reproduce important observed features while differing in their assumptions and predictions.