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  An improved multi-ridge fitting method for ring-diagram helioseismic analysis

Nagashima, K., Birch, A., Schou, J., Hindman, B. W., & Gizon, L. (2020). An improved multi-ridge fitting method for ring-diagram helioseismic analysis. Astronomy and Astrophysics, 633: A109. doi:10.1051/0004-6361/201936662.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0005-862F-0 Version Permalink: http://hdl.handle.net/21.11116/0000-0005-8630-D
Genre: Journal Article

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 Creators:
Nagashima, Kaori1, Author              
Birch, Aaron1, Author              
Schou, Jesper1, Author              
Hindman, Bradley W., Author
Gizon, Laurent1, Author              
Affiliations:
1Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832287              

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Free keywords: Sun: helioseismology / methods: data analysis
 Abstract: Context. There is a wide discrepancy in current estimates of the strength of convection flows in the solar interior obtained using different helioseismic methods applied to observations from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory. The cause for these disparities is not known. Aims. As one step in the effort to resolve this discrepancy, we aim to characterize the multi-ridge fitting code for ring-diagram helioseismic analysis that is used to obtain flow estimates from local power spectra of solar oscillations. Methods. We updated the multi-ridge fitting code developed by Greer et al. (2014, Sol. Phys., 289, 2823) to solve several problems we identified through our inspection of the code. In particular, we changed the (1) merit function to account for the smoothing of the power spectra, (2) model for the power spectrum, and (3) noise estimates. We used Monte Carlo simulations to generate synthetic data and to characterize the noise and bias of the updated code by fitting these synthetic data. Results. The bias in the output fit parameters, apart from the parameter describing the amplitude of the p-mode resonances in the power spectrum, is below what can be measured from the Monte-Carlo simulations. The amplitude parameters are underestimated; this is a consequence of choosing to fit the logarithm of the averaged power. We defer fixing this problem as it is well understood and not significant for measuring flows in the solar interior. The scatter in the fit parameters from the Monte-Carlo simulations is well-modeled by the formal error estimates from the code. Conclusions. We document and demonstrate a reliable multi-ridge fitting method for ring-diagram analysis. The differences between the updated fitting results and the original results are less than one order of magnitude and therefore we suspect that the changes will not eliminate the aforementioned orders-of-magnitude discrepancy in the amplitude of convective flows in the solar interior.

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Language(s): eng - English
 Dates: 2020
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1051/0004-6361/201936662
 Degree: -

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Title: Astronomy and Astrophysics
Source Genre: Journal
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Publ. Info: Les Ulis Cedex A France : EDP Sciences
Pages: - Volume / Issue: 633 Sequence Number: A109 Start / End Page: - Identifier: -