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Understanding the governing mechanism of solar magnetism remains anoutstanding challenge in astrophysics. Seismology is the most compellingtechnique with which to infer the internal properties of the Sun and stars.Waves in the Sun, nominally acoustic, are sensitive to the emergence andcyclical strengthening of magnetic field, evidenced by measured changes inresonant oscillation frequencies that are correlated with the solar cycle. Theinference of internal Lorentz stresses from these measurements has thepotential to significantly advance our appreciation of the dynamo. Indeed,seismological inverse theory for the Sun is well understood for perturbationsin composition, thermal structure and flows but, is not fully developed formagnetism, owing to the complexity of the ideal magnetohydrodynamic (MHD)equation. Invoking first-Born perturbation theory to characterize departuresfrom spherically symmetric hydrostatic models of the Sun and applying thenotation of generalized spherical harmonics, we calculate sensitivity functionsof seismic measurements to the general time-varying Lorentz stress tensor. Wefind that eigenstates of isotropic (i.e. acoustic only) background models aredominantly sensitive to isotropic deviations in the stress tensor and much moreweakly so to anisotropic stresses (and therefore challenging to infer). Theapple cannot fall far from the tree.

Seismic sensitivity of Normal-mode Coupling to Lorentz stresses in the Sun