Inversions for Deep Solar Meridional Flow Using Spherical Born Kernels

The solar meridional flow is a crucial ingredient in modern dynamo theory. Seismic estimates of this flow have, however, been contradictory in deeper layers below about \(0.9\,R_\odot\). Results from time-distance helioseismology have so far been obtained using the ray approximation. Here, we perfor...

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Bibliographic Details
Published in:arXiv.org 2017-07
Main Authors: Böning, Vincent G A, Roth, Markus, Jackiewicz, Jason, Shukur Kholikov
Format: Article
Language:English
Subjects:
Approximation
Born approximation
Covariance matrix
Crosstalk
Dynamo theory
Helioseismology
Inversions
Kernels
Mathematical analysis
Meridional flow
Regularization
Return flow
Singular value decomposition
Southern Hemisphere
Travel time
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Summary:The solar meridional flow is a crucial ingredient in modern dynamo theory. Seismic estimates of this flow have, however, been contradictory in deeper layers below about \(0.9\,R_\odot\). Results from time-distance helioseismology have so far been obtained using the ray approximation. Here, we perform inversions using the Born approximation. The initial result is similar to the result previously obtained by Jackiewicz et al. (2015) using ray kernels while using the same set of GONG data and the SOLA inversion technique. However, we show that the assumption of uncorrelated measurements used in earlier studies may lead to inversion errors being underestimated by a factor of about two to four. In a second step, refined inversions are performed using the full covariance matrix and a regularization for cross-talk. As the results are found to depend on the threshold used in the singular value decomposition, they were obtained for a medium threshold (\(10^{-7}-10^{-5}\), about 50% of the values used) and a threshold lower by a factor of 10 (about 70% of the values used). The result obtained with the medium threshold is again similar to the original, with less latitudinal variation. However, using the lower threshold, the inverted flow in the southern hemisphere shows two or three cells stacked radially depending on the associated radial flows. Both the single-cell and the multi-cell profiles are consistent with the measured travel times. All our results confirm a shallow return flow at about \(0.9\,R_\odot\).
ISSN:2331-8422
DOI:10.48550/arxiv.1707.08803