Seismic halos around active regions

A magnetohydrodynamic theory

Shravan Hanasoge

    Research output: Contribution to journalArticle

    Abstract

    Comprehending the manner in which magnetic fields affect propagating waves is a first step toward constructing accurate helioseismic models of active region subsurface structure and dynamics. Here we present a numerical method for computing the linear interaction of waves with magnetic fields embedded in a solar-like stratified background. The ideal magnetohydrodynamic (MHD) equations are solved in a three-dimensional box that straddles the solar surface, extending from 35 Mm below the photosphere to 1.2 Mm into the atmosphere. One of the challenges in performing these simulations involves generating a magnetohydrostatic (MHS) state wherein the stratification assumes horizontal inhomogeneity in addition to the strong vertical stratification associated with the near-surface layers. Keeping in mind that the aim of this effort is to understand and characterize linear MHD interactions, we discuss a means of computing statically consistent background states. Power maps computed from simulations of waves interacting with thick flux tubes that have peak photospheric field strengths of 600 and 3000 G are presented. Strong modal power reduction in the "umbral" regions of the flux tube enveloped by a halo of increased wave power is seen in the simulations with the thick flux tubes. These enhancements are also seen in Doppler velocity power maps of active regions observed in the Sun, which leads us to propose that the halo has MHD underpinnings.

    Original languageEnglish (US)
    Pages (from-to)1457-1466
    Number of pages10
    JournalAstrophysical Journal
    Volume680
    Issue number2
    DOIs
    StatePublished - Jun 20 2008

    Fingerprint

    magnetohydrodynamics
    halos
    stratification
    tubes
    magnetic field
    simulation
    wave power
    magnetohydrostatics
    inhomogeneity
    numerical method
    surface layer
    photosphere
    magnetic fields
    boxes
    field strength
    surface layers
    sun
    atmosphere
    interactions
    atmospheres

    Keywords

    • Hydrodynamics
    • Sun: helioseismology
    • Sun: interior
    • Sun: oscillations
    • Waves

    ASJC Scopus subject areas

    • Nuclear and High Energy Physics
    • Space and Planetary Science

    Cite this

    Seismic halos around active regions : A magnetohydrodynamic theory. / Hanasoge, Shravan.

    In: Astrophysical Journal, Vol. 680, No. 2, 20.06.2008, p. 1457-1466.

    Research output: Contribution to journalArticle

    Hanasoge, Shravan. / Seismic halos around active regions : A magnetohydrodynamic theory. In: Astrophysical Journal. 2008 ; Vol. 680, No. 2. pp. 1457-1466.
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