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-cycletimescale variability of the total irradiance, is produced by structuraladjustments of the solar interior. Assuming these adjustments are induced byvariations of internal magnetic fields, we use measurements of the totalirradiance and effective temperature over the period from 1978 to 1992, toinfer the magnitude and location of the magnetic field. Using an updatedstellar evolution model, which includes magnetic fields, we find that theobservations can be explained by fields whose peak values range from 120k to2.3k gauss, located in the convection zone between $0.959R_{\sun}$ and$0.997R_{\sun}$, respectively. The corresponding maximal radius changes, are 17km when the magnetic field is located at $0.959R_{\sun}$ and 3 km when it islocated at $0.997R_{\sun}$. At these depths, the $W$ parameter(defined by$\Delta \ln R / \Delta \ln L$, where $R$ and $L$ are the radius and luminosity)ranges from 0.02 to 0.006. All these predictions are consistent withhelioseismology and recent measurements carried out by the MDI experiment onSOHO.Comment: 8 pages, 8 figures, to appear in Ap