Computational helioseismology in the frequency domain: Acoustic waves in axisymmetric solar models with flows

Laurent Gizon, Hélène Barucq, Marc Duruflé, Chris S. Hanson, Michael Leguèbe, Aaron C. Birch, Juliette Chabassier, Damien Fournier, Thorsten Hohage, Emanuele Papini

Research output: Contribution to journalArticle

Abstract

Context. Local helioseismology has so far relied on semi-analytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Aims. Here we propose a convenient framework for numerically solving the forward problem of time-distance helioseismology in the frequency domain. The fundamental quantity to be computed is the cross-covariance of the seismic wavefield. Methods. We choose sources of wave excitation that enable us to relate the cross-covariance of the oscillations to the Green's function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the effects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green's function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a high-order finite-element method to solve the 2D wave equation in frequency space. The computation is embarrassingly parallel, with each frequency and each azimuthal order solved independently on a computer cluster. Results. We compute travel-time sensitivity kernels in spherical geometry for flows, sound speed, and density perturbations under the first Born approximation. Convergence tests show that travel times can be computed with a numerical precision better than one millisecond, as required by the most precise travel-time measurements. Conclusions. The method presented here is computationally efficient and will be used to interpret travel-time measurements in order to infer, e.g., the large-scale meridional flow in the solar convection zone. It allows the implementation of (full-waveform) iterative inversions, whereby the axisymmetric background model is updated at each iteration.

Original languageEnglish (US)
Article numberA35
JournalAstronomy and Astrophysics
Volume600
DOIs
StatePublished - Apr 1 2017

Fingerprint

helioseismology
acoustic wave
travel time
travel
acoustics
Green function
wave equation
wave equations
Green's functions
time measurement
perturbation
meridional flow
solar interior
Born approximation
sensitivity
wave excitation
finite element method
iteration
symmetry
analytical method

Keywords

  • Sun: Helioseismology
  • Sun: Interior
  • Sun: Oscillations

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Computational helioseismology in the frequency domain : Acoustic waves in axisymmetric solar models with flows. / Gizon, Laurent; Barucq, Hélène; Duruflé, Marc; Hanson, Chris S.; Leguèbe, Michael; Birch, Aaron C.; Chabassier, Juliette; Fournier, Damien; Hohage, Thorsten; Papini, Emanuele.

In: Astronomy and Astrophysics, Vol. 600, A35, 01.04.2017.

Research output: Contribution to journalArticle

Gizon, L, Barucq, H, Duruflé, M, Hanson, CS, Leguèbe, M, Birch, AC, Chabassier, J, Fournier, D, Hohage, T & Papini, E 2017, 'Computational helioseismology in the frequency domain: Acoustic waves in axisymmetric solar models with flows', Astronomy and Astrophysics, vol. 600, A35. https://doi.org/10.1051/0004-6361/201629470
Gizon, Laurent ; Barucq, Hélène ; Duruflé, Marc ; Hanson, Chris S. ; Leguèbe, Michael ; Birch, Aaron C. ; Chabassier, Juliette ; Fournier, Damien ; Hohage, Thorsten ; Papini, Emanuele. / Computational helioseismology in the frequency domain : Acoustic waves in axisymmetric solar models with flows. In: Astronomy and Astrophysics. 2017 ; Vol. 600.
@article{53637990456b491aa9c5abf9465f25c8,
title = "Computational helioseismology in the frequency domain: Acoustic waves in axisymmetric solar models with flows",
abstract = "Context. Local helioseismology has so far relied on semi-analytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Aims. Here we propose a convenient framework for numerically solving the forward problem of time-distance helioseismology in the frequency domain. The fundamental quantity to be computed is the cross-covariance of the seismic wavefield. Methods. We choose sources of wave excitation that enable us to relate the cross-covariance of the oscillations to the Green's function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the effects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green's function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a high-order finite-element method to solve the 2D wave equation in frequency space. The computation is embarrassingly parallel, with each frequency and each azimuthal order solved independently on a computer cluster. Results. We compute travel-time sensitivity kernels in spherical geometry for flows, sound speed, and density perturbations under the first Born approximation. Convergence tests show that travel times can be computed with a numerical precision better than one millisecond, as required by the most precise travel-time measurements. Conclusions. The method presented here is computationally efficient and will be used to interpret travel-time measurements in order to infer, e.g., the large-scale meridional flow in the solar convection zone. It allows the implementation of (full-waveform) iterative inversions, whereby the axisymmetric background model is updated at each iteration.",
keywords = "Sun: Helioseismology, Sun: Interior, Sun: Oscillations",
author = "Laurent Gizon and H{\'e}l{\`e}ne Barucq and Marc Durufl{\'e} and Hanson, {Chris S.} and Michael Legu{\`e}be and Birch, {Aaron C.} and Juliette Chabassier and Damien Fournier and Thorsten Hohage and Emanuele Papini",
year = "2017",
month = "4",
day = "1",
doi = "10.1051/0004-6361/201629470",
language = "English (US)",
volume = "600",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",

}

TY - JOUR

T1 - Computational helioseismology in the frequency domain

T2 - Acoustic waves in axisymmetric solar models with flows

AU - Gizon, Laurent

AU - Barucq, Hélène

AU - Duruflé, Marc

AU - Hanson, Chris S.

AU - Leguèbe, Michael

AU - Birch, Aaron C.

AU - Chabassier, Juliette

AU - Fournier, Damien

AU - Hohage, Thorsten

AU - Papini, Emanuele

PY - 2017/4/1

Y1 - 2017/4/1

N2 - Context. Local helioseismology has so far relied on semi-analytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Aims. Here we propose a convenient framework for numerically solving the forward problem of time-distance helioseismology in the frequency domain. The fundamental quantity to be computed is the cross-covariance of the seismic wavefield. Methods. We choose sources of wave excitation that enable us to relate the cross-covariance of the oscillations to the Green's function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the effects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green's function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a high-order finite-element method to solve the 2D wave equation in frequency space. The computation is embarrassingly parallel, with each frequency and each azimuthal order solved independently on a computer cluster. Results. We compute travel-time sensitivity kernels in spherical geometry for flows, sound speed, and density perturbations under the first Born approximation. Convergence tests show that travel times can be computed with a numerical precision better than one millisecond, as required by the most precise travel-time measurements. Conclusions. The method presented here is computationally efficient and will be used to interpret travel-time measurements in order to infer, e.g., the large-scale meridional flow in the solar convection zone. It allows the implementation of (full-waveform) iterative inversions, whereby the axisymmetric background model is updated at each iteration.

AB - Context. Local helioseismology has so far relied on semi-analytical methods to compute the spatial sensitivity of wave travel times to perturbations in the solar interior. These methods are cumbersome and lack flexibility. Aims. Here we propose a convenient framework for numerically solving the forward problem of time-distance helioseismology in the frequency domain. The fundamental quantity to be computed is the cross-covariance of the seismic wavefield. Methods. We choose sources of wave excitation that enable us to relate the cross-covariance of the oscillations to the Green's function in a straightforward manner. We illustrate the method by considering the 3D acoustic wave equation in an axisymmetric reference solar model, ignoring the effects of gravity on the waves. The symmetry of the background model around the rotation axis implies that the Green's function can be written as a sum of longitudinal Fourier modes, leading to a set of independent 2D problems. We use a high-order finite-element method to solve the 2D wave equation in frequency space. The computation is embarrassingly parallel, with each frequency and each azimuthal order solved independently on a computer cluster. Results. We compute travel-time sensitivity kernels in spherical geometry for flows, sound speed, and density perturbations under the first Born approximation. Convergence tests show that travel times can be computed with a numerical precision better than one millisecond, as required by the most precise travel-time measurements. Conclusions. The method presented here is computationally efficient and will be used to interpret travel-time measurements in order to infer, e.g., the large-scale meridional flow in the solar convection zone. It allows the implementation of (full-waveform) iterative inversions, whereby the axisymmetric background model is updated at each iteration.

KW - Sun: Helioseismology

KW - Sun: Interior

KW - Sun: Oscillations

UR - http://www.scopus.com/inward/record.url?scp=85016562198&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85016562198&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201629470

DO - 10.1051/0004-6361/201629470

M3 - Article

AN - SCOPUS:85016562198

VL - 600

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

M1 - A35

ER -