Seismic sensitivity of normal-mode coupling to Lorentz stresses in the Sun

Shravan Hanasoge

    Research output: Contribution to journalArticle

    Abstract

    Understanding the governing mechanism of solar magnetism remains an outstanding challenge in astrophysics. Seismology is the most compelling technique to infer the internal properties of the Sun and stars. Waves in the Sun, nominally acoustic, are sensitive to the emergence and cyclical strengthening of magnetic field, evidenced by measured changes in resonant oscillation frequencies that are correlated with the solar cycle. The inference of internal Lorentz stresses from these measurements has the potential to significantly advance our appreciation of the dynamo. Indeed, seismological inverse theory for the Sun is well understood for perturbations in composition, thermal structure and flows but, is not fully developed for magnetism, owing to the complexity of the ideal magnetohydrodynamic (MHD) equation. Invoking first-Born perturbation theory to characterize departures from spherically symmetric hydrostatic models of the Sun and applying the notation of generalized spherical harmonics, we calculate sensitivity functions of seismicmeasurements to the general time-varying Lorentz stress tensor. We find that eigenstates of isotropic (i.e. acoustic only) background models are dominantly sensitive to isotropic deviations in the stress tensor and much more weakly than anisotropic stresses (and therefore challenging to infer). The apple cannot fall far from the tree.

    Original languageEnglish (US)
    Article numberstx1342
    Pages (from-to)2780-2790
    Number of pages11
    JournalMonthly Notices of the Royal Astronomical Society
    Volume470
    Issue number3
    DOIs
    StatePublished - Sep 21 2017

    Fingerprint

    coupled modes
    sun
    sensitivity
    stress tensors
    acoustics
    perturbation
    seismology
    astrophysics
    spherical harmonics
    thermal structure
    solar cycles
    hydrostatics
    magnetohydrodynamics
    inference
    solar cycle
    eigenvectors
    coding
    perturbation theory
    oscillation
    magnetic field

    Keywords

    • Hydrodynamics
    • Sun: helioseismology
    • Sun: interior
    • Sun: oscilla-tions
    • Waves

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

    Cite this

    Seismic sensitivity of normal-mode coupling to Lorentz stresses in the Sun. / Hanasoge, Shravan.

    In: Monthly Notices of the Royal Astronomical Society, Vol. 470, No. 3, stx1342, 21.09.2017, p. 2780-2790.

    Research output: Contribution to journalArticle

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