Direct measurement of-travel-time kernels for helioseismology

T. L. Duvall, A. C. Birch, Laurent Gizon

Research output: Contribution to journalArticle

Abstract

Solar f-modes are surface gravity waves that propagate horizontally in a thin layer near the photosphere with a dispersion relation approximately that of deep water waves. At the power maximum near frequency ω/2π = 3 mHz, the wavelength of 5 Mm is large enough for various wave scattering properties to be observable. Gizon & Birch have calculated spatial kernels for scattering in the Born approximation. In this paper, using isolated small magnetic features as approximate point scatterers, a linear-response kernel has been measured. In addition, the kernel has been estimated by deconvolving the magnetograms from the travel-time maps. The observed kernel is similar to the theoretical kernel for wave damping computed by Gizon & Birch: it includes elliptical and hyperbolic features. This is the first observational evidence to suggest that it is appropriate to use the Born approximation to compute kernels (as opposed to the ray approximation). Furthermore, the observed hyperbolic features confirm that it is important to take into account scattering of the waves coming from distant source locations (as opposed to the single-source approximation). The observed kernel is due to a superposition of the direct and indirect effects of the magnetic field. A simple model that includes both monopole and dipole scattering compares favorably with the data. This new technique appears to be promising to study how seismic waves interact with magnetic flux tubes.

Original languageEnglish (US)
Pages (from-to)553-559
Number of pages7
JournalAstrophysical Journal
Volume646
Issue numberI
DOIs
StatePublished - Jul 20 2006

Fingerprint

helioseismology
travel time
travel
Born approximation
scattering
wave damping
wave scattering
water wave
seismic wave
gravity wave
surface wave
water waves
magnetic signatures
deep water
seismic waves
photosphere
gravity waves
approximation
monopoles
magnetic field

Keywords

  • Methods: data analysis
  • Scattering
  • Sun: helioseismology
  • Sun: magnetic fields
  • Ttechniques: image processing

ASJC Scopus subject areas

  • Space and Planetary Science
  • Nuclear and High Energy Physics

Cite this

Direct measurement of-travel-time kernels for helioseismology. / Duvall, T. L.; Birch, A. C.; Gizon, Laurent.

In: Astrophysical Journal, Vol. 646, No. I, 20.07.2006, p. 553-559.

Research output: Contribution to journalArticle

Duvall, T. L. ; Birch, A. C. ; Gizon, Laurent. / Direct measurement of-travel-time kernels for helioseismology. In: Astrophysical Journal. 2006 ; Vol. 646, No. I. pp. 553-559.
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