Finite-frequency sensitivity kernels in spherical geometry for time-distance helioseismology

Abstract

The inference of internal properties of the Sun from surface measurements of wave travel times is the goal of time-distance helioseismology. A critical step toward the accurate interpretation of travel-time shifts is the computation of sensitivity functions linking seismic measurements to internal structure. Here we calculate finite-frequency sensitivity kernels in spherical geometry for two-point travel-time measurements. We numerically build Green's function by solving for it at each frequency and spherical-harmonic degree and summing over all these pieces. These computations are performed in parallel ("embarrassingly"), thereby achieving significant speedup in wall-clock time. Kernels are calculated by invoking the first-order Born approximation connecting deviations in the wavefield to perturbations in the operator. Validated flow kernels are shown to produce travel times within 0.47% of the true value for uniform flows up to 750 m/s. We find that travel-time can be obtained with errors of 1 millisecond or less for flows having magnitudes similar to meridional circulation. Alongside flows, we also compute and validate sensitivity kernel for sound-speed perturbations. These accurate sensitivity kernels might improve the current inferences of sub-surface flows significantly.

32 pages, 10 figures, accepted for publication in ApJ

References in corpus (11)

• Detection of Equatorward Meridional Flow and Evidence of Double-Cell Meridional Circulation inside the Sun
• Local Helioseismology: Three Dimensional Imaging of the Solar Interior
• Meridional circulation in the solar convection zone: time-distance helioseismic inferences from four years of HMI/SDO observations
• Seismic Sounding of Convection in the Sun
• Meridional Flow in the Solar Convection Zone II: Helioseismic Inversions of GONG Data
• Linear Sensitivity of Helioseismic Travel Times to Local Flows
• Computational helioseismology in the frequency domain: acoustic waves in axisymmetric solar models with flows
• The Adjoint Method Applied to Time-Distance Helioseismology
• Time-distance helioseismology: Sensitivity of f-mode travel times to flows
• Sensitivity Kernels for Flows in Time-Distance Helioseismology: Extension to Spherical Geometry
• Interpretation of Helioseismic Travel Times - Sensitivity to Sound Speed, Pressure, Density, and Flows

Cited by in corpus (8)

• Helioseismic inversion to infer depth profile of solar meridional flow using spherical Born kernels
• Sensitivity kernels for time-distance helioseismology: efficient computation for spherically-symmetric solar models
• Assessing the Observability of Deep Meridional Flow Cells in the Solar Interior
• A general formulation for computing spherical helioseismic sensitivity kernels while incorporating systematical effects
• 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
• Helioseismic finite-frequency sensitivity kernels for flows in spherical geometry including systematic effects
• Numerical evaluation of time-distance helioseismic sensitivity kernels in spherical geometry