The variability of solar radiance over a solar cycle is thought the result of a delicate balance between the blocking effect of sunspots and the positive contribution of bright plage and network faculae. Although the net effect is small, it must imply structural changes of the Sun or partial layers of it as an unavoidable consequence of the virial theorem. Using a general form of the virial theorem for continua including the magnetic field it is shown, how solar radiance variability might be connected to a deeply seated flux-tube dynamo and how this connection is established on a hydrodynamical time-scale.
- http://www.kis.uni-freiburg.de/~steiner/#sec4 - Contrib. to appear in proceeding of IAU Symp. 223