Validated helioseismic inversions for 3D vector flows

M. Švanda, Laurent Gizon, Shravan Hanasoge, S. D. Ustyugov

Research output: Contribution to journalArticle

Abstract

Context. According to time-distance helioseismology, information about internal fluid motions is encoded in the travel times of solar waves. The inverse problem consists of inferring three-dimensional vector flows from a set of travel-time measurements. While only few tests of the inversions have been done, it is known that the retrieval of the small-amplitude vertical flow velocities is problematic. A thorough study of biases and noise has not been carried out in realistic conditions. Aims. Here we investigate the potential of time-distance helioseismology to infer three-dimensional convective velocities in the near-surface layers of the Sun. We developed a new subtractive optimally localised averaging (SOLA) code suitable for pipeline pseudo-automatic processing. Compared to its predecessor, the code was improved by accounting for additional constraints in order to get the right answer within a given noise level. The main aim of this study is to validate results obtained by our inversion code. Methods. We simulate travel-time maps using a snapshot from a numerical simulation of solar convective flows, realistic Born travel-time sensitivity kernels, and a realistic model of travel-time noise. These synthetic travel times are inverted for flows and the results compared with the known input flow field. Additional constraints are implemented in the inversion: cross-talk minimization between flow components and spatial localization of inversion coefficients. Results. Using modes f, p1 through p 4, we show that horizontal convective flow velocities can be inferred without bias, at a signal-to-noise ratio greater than one in the top 3.5 Mm, provided that observations span at least four days. The vertical component of velocity (vz), if it were to be weak, is more difficult to infer and is seriously affected by cross-talk from horizontal velocity components. We emphasise that this cross-talk must be explicitly minimised in order to retrieve vz in the top 1 Mm. We also show that statistical averaging over many different areas of the Sun allows for reliably measuring of average properties of all three flow components in the top 5.5 Mm of the convection zone.

Original languageEnglish (US)
Article numberA148
JournalAstronomy and Astrophysics
Volume530
DOIs
StatePublished - Jun 2 2011

Fingerprint

travel time
travel
inversions
helioseismology
convective flow
flow velocity
sun
inverse problem
signal-to-noise ratio
flow field
inversion
surface layer
retrieval
convection
surface layers
flow distribution
signal to noise ratios
time measurement
fluid
optimization

Keywords

  • Methods: data analysis
  • Sun: helioseismology
  • Sun: oscillations

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Validated helioseismic inversions for 3D vector flows. / Švanda, M.; Gizon, Laurent; Hanasoge, Shravan; Ustyugov, S. D.

In: Astronomy and Astrophysics, Vol. 530, A148, 02.06.2011.

Research output: Contribution to journalArticle

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