Inversions for Deep Solar Meridional Flow Using Spherical Born Kernels

Abstract

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 $0.9R_{\odot }$. 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 $0.9R_{\odot }$.

15 pages, 15 figures, accepted for publication in The Astrophysical Journal

References in corpus (29)

• Detection of Equatorward Meridional Flow and Evidence of Double-Cell Meridional Circulation inside the Sun
• Acoustic tomography of solar convective flows and structures
• Global helioseismic evidence for a deeply penetrating Solar meridional flow consisting of multiple flow cells
• Systematic Center-to-Limb Variation in Measured Helioseismic Travel Times and Its Effect on Inferences of Solar Interior Meridional Flows
• Is a deep one-cell meridional circulation essential for the flux transport Solar Dynamo?
• Meridional circulation in the solar convection zone: time-distance helioseismic inferences from four years of HMI/SDO observations
• Effects of Asymmetric Flows in Solar Convection on Oscillation Modes
• Supergranules as Probes of the Sun's Meridional Circulation
• Meridional Flow in the Solar Convection Zone II: Helioseismic Inversions of GONG Data
• Time--Distance Helioseismology Data Analysis Pipeline for Helioseismic and Magnetic Imager onboard Solar Dynamics Observatory (SDO/HMI) and Its Initial Results
• Linear Sensitivity of Helioseismic Travel Times to Local Flows
• Computational helioseismology in the frequency domain: acoustic waves in axisymmetric solar models with flows
• High-resolution mapping of flows in the solar interior: Fully consistent OLA inversion of helioseismic travel times
• Validated helioseismic inversions for 3-D vector flows
• Meridional Flow in the Solar Convection Zone I: Measurements from GONG Data
• Multi-Channel Three-Dimensional SOLA Inversion for Local Helioseismology
• Comparison of solar surface flows inferred from time--distance helioseismology and coherent structure tracking using HMI/SDO observations
• Validating Time-Distance Helioseismology With Realistic Quiet Sun Simulations
• Tomography of plasma flows in the upper solar convection zone using time--distance inversion combining ridge and phase-speed filtering
• Generalization of the noise model for time-distance helioseismology
• Comparison of acoustic travel-time measurement of solar meridional circulation from SDO/HMI and SOHO/MDI
• Sensitivity Kernels for Flows in Time-Distance Helioseismology: Extension to Spherical Geometry
• Solar wave-field simulation for testing prospects of helioseismic measurements of deep meridional flows
• Helioseismic Investigation of Modeled and Observed Supergranule Structure
• Time-Distance Helioseismology of Two Realistic Sunspot Simulations
• Verification of the helioseismic Fourier-Legendre analysis for meridional flow measurements
• Pinsker estimators for local helioseismology
• Validation of Spherical Born Approximation Sensitivity Functions for Measuring Deep Solar Meridional Flow
• Time--distance inversions for horizontal and vertical flows on supergranular scales applied to MDI and HMI data

Cited by in corpus (15)

• The Solar Orbiter mission -- Science overview
• The Polarimetric and Helioseismic Imager on Solar Orbiter
• Results from EDGES High-Band: I. Constraints on Phenomenological Models for the Global $21$ cm Signal
• Solar meridional circulation from twenty-one years of SOHO/MDI and SDO/HMI observations: Helioseismic travel times and forward modeling in the ray approximation
• On the Origin of Solar Torsional Oscillations and Extended Solar Cycle
• Possible Atmospheric Diversity of Low Mass Exoplanets, some Central Aspects
• Helioseismic inversion to infer depth profile of solar meridional flow using spherical Born kernels
• On the origin of the double cell meridional circulation in the solar convection zone
• Solar dynamo cycle variations with a rotational period
• Nonkinematic solar dynamo models with double-cell meridional circulation
• Forward Modeling Helioseismic Signatures of One- and Two-cell Meridional Circulation
• Assessing the Observability of Deep Meridional Flow Cells in the Solar Interior
• Helioseismological determination of the subsurface spatial spectrum of solar convection: Demonstration using numerical simulations
• Computing Helioseismic Sensitivity Kernels for the Sun's Large-Scale Internal Flows using Global-Scale Wave-Propagation Simulations
• Global simulations of stellar dynamos