Measurements of Solar Irradiance and Effective Temperature as a Probe of Solar Interior Magnetic Fields

We argue that a variety of solar data suggest that the activity-cycle timescale variability of the total irradiance is produced by structural adjustments of the solar interior. On the assumption that these adjustments are induced by variations of internal magnetic fields, we use measurements of the total irradiance and effective temperature over the period from 1978 to 1992 to infer the magnitude and location of the magnetic field. Based on an updated stellar evolution model with magnetic fields taken into account, we find that the observations can be explained by fields whose peak values range from 120k to 2.3k gauss, located in the convection zone at depths ranging from r = 0.950R⊙ to 0.997R⊙, respectively. The corresponding maximal radius changes range from 19 to 3 km, and W = d lnR/d lnL from 0.03 to 0.006. All these predictions are consistent with helioseismology and recent measurements carried out by the MDI experiment on SOHO. Subject headings: Sun: interior — Sun: magnetic fields