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  Atmospheric-radiation boundary conditions for high-frequency waves in time-distance helioseismology

Fournier, D., Leguèbe, M., Hanson, C. S., Gizon, L., Barucq, H., Chabassier, J., et al. (2017). Atmospheric-radiation boundary conditions for high-frequency waves in time-distance helioseismology. Astronomy and Astrophysics, 608: A109. doi:10.1051/0004-6361/201731283.

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 Creators:
Fournier, Damien1, Author              
Leguèbe, Michael1, Author              
Hanson, Chris S.1, Author              
Gizon, Laurent1, Author              
Barucq, H., Author
Chabassier, J., Author
Duruflé, M., Author
Affiliations:
1Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832287              

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 MPIS_GROUPS: Solar and Stellar Interiors
 MPIS_PROJECTS: SDO: German Data Center
 Abstract: The temporal covariance between seismic waves measured at two locations on the solar surface is the fundamental observable in time-distance helioseismology. Above the acoustic cut-off frequency (~5.3 mHz), waves are not trapped in the solar interior and the covariance function can be used to probe the upper atmosphere. We wish to implement appropriate radiative boundary conditions for computing the propagation of high-frequency waves in the solar atmosphere. We consider recently developed and published radiative boundary conditions for atmospheres in which sound-speed is constant and density decreases exponentially with radius. We compute the cross-covariance function using a finite element method in spherical geometry and in the frequency domain. The ratio between first- and second-skip amplitudes in the time-distance diagram is used as a diagnostic to compare boundary conditions and to compare with observations. We find that a boundary condition applied 500 km above the photosphere and derived under the approximation of small angles of incidence accurately reproduces the “infinite atmosphere” solution for high-frequency waves. When the radiative boundary condition is applied 2 Mm above the photosphere, we find that the choice of atmospheric model affects the time-distance diagram. In particular, the time-distance diagram exhibits double-ridge structure when using a Vernazza Avrett Loeser atmospheric model.

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Language(s): eng - English
 Dates: 2018-01-302017
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1051/0004-6361/201731283
 Degree: -

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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
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Publ. Info: Berlin : Springer-Verlag
Pages: - Volume / Issue: 608 Sequence Number: A109 Start / End Page: - Identifier: ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1