Subsurface magnetic fields from helioseismology

Abstract

Using even-order frequency splitting coefficients of global p-modes it is possible to infer the magnetic field in the solar interior as a function of radial distance and latitude. Results obtained using GONG and MDI data are discussed. While there is some signal of a possible magnetic field in the convection zone, there is little evidence for any temporal variation of the magnetic field in the solar interior. Limits on possible magnetic field in the solar core are also discussed. It is generally believed that the solar dynamo is located in the tachocline region. Seismic studies do not show any significant temporal variation in the tachocline region, though a significant latitudinal variation in the properties of the tachocline are found. There is some evidence to suggest that the latitudinal variation is not continuous and the tachocline may consist of two parts.