Published online by Cambridge University Press: 12 April 2016
Dynamical and thermal modulation of the internal structure of the Sun can be manifest at the surface as changes in irradiance and radius. The relative magnitudes of these changes could provide a diagnostic of at least the location of the primary modulation, if only the mechanism were known. Variations of the frequencies of solar oscillations offer additional potentially valuable diagnostics, but unfortunately at present the mechanisms causing those variations and their relation to the structural and irradiance changes are not yet understood. In this lecture I shall review some of the theoretical conjectures that have been put forward to explain the observations.