Seismic probes of solar interior magnetic structure

Abstract

Sunspots are prominent manifestations of solar magnetoconvection and imaging their subsurface structure is an outstanding problem of wide physical importance. Travel times of seismic waves that propagate through these structures are typically used as inputs to inversions. Despite the presence of strongly anisotropic magnetic waveguides, these measurements have always been interpreted in terms of changes to isotropic wavespeeds and flow-advection related Doppler shifts. Here, we employ PDE-constrained optimization to determine the appropriate parameterization of the structural properties of the magnetic interior. Seven different wavespeeds fully characterize helioseismic wave propagation: the isotropic sound speed, a Doppler-shifting flow-advection velocity and an anisotropic magnetic velocity. The structure of magnetic media is sensed by magnetoacoustic slow and fast modes and Alfvén waves, each of which propagates at a different wavespeed. We show that even in the case of weak magnetic fields, significant errors may be incurred if these anisotropies are not accounted for in inversions. Translation invariance is demonstrably lost. These developments render plausible the accurate seismic imaging of magnetoconvection in the Sun.

4 pages, 4 figures, accepted Physical Review Letters

References in corpus (4)

• Helioseismology of Sunspots: Confronting Observations with Three-Dimensional MHD Simulations of Wave Propagation
• Seismic Halos Around Active Regions: An MHD Theory
• Scattering of acoustic waves by a magnetic cylinder
• Impact of Locally Suppressed Wave sources on helioseismic travel times

Cited by in corpus (9)

• Seismic Sounding of Convection in the Sun
• Helioseismology of sunspots: how sensitive are travel times to the Wilson depression and to the subsurface magnetic field?
• Full Waveform Inversion of Solar Interior Flows
• The Quest to Understand Supergranulation and Large-Scale Convection in the Sun
• Helioseismic Holography of Simulated Sunspots: dependence of the travel time on magnetic field strength and Wilson depression
• Seismic sensitivity of Normal-mode Coupling to Lorentz stresses in the Sun
• Directional Time-Distance Probing of Model Sunspot Atmospheres
• Sensitivity kernels for inferring Lorentz stresses from normal-mode frequency splittings in the Sun
• The Current State-Of-The-Art In Active Region Seismology