“Hare and Hounds” Tests of Helioseismic Holography

Birch, A. C.; Parchevsky, K. V.; Braun, D. C.; Kosovichev, A. G.

doi:10.1007/s11207-011-9799-1

Cited by 11 publications

(16 citation statements)

References 40 publications

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“…The simulations of wave propagation in a magnetohydrostatic (MHS) model by Moradi et al (2009) also reproduced this behavior. Later, Birch et al (2011) performed some tests of helioseismic holography using two cases of non-magnetic models with the wave-speed structures inferred from observations, including the twolayer model (Kosovichev et al 2000) and a one-layer model with a near-surface increase of the sound speed (Fan et al 1995). Their inversions were able to qualitatively recover the structure of the background models.…”

Section: Introductionmentioning

confidence: 99%

Helioseismic Holography of Simulated Sunspots: Magnetic and Thermal Contributions to Travel Times

Felipe

Braun

Crouch

et al. 2016

ApJ

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Wave propagation through sunspots involves conversion between waves of acoustic and magnetic character. In addition, the thermal structure of sunspots is very different than that of the quiet Sun. As a consequence, the interpretation of local helioseismic measurements of sunspots has long been a challenge. With the aim of understanding these measurements, we carry out numerical simulations of wave propagation through sunspots. Helioseismic holography measurements made from the resulting simulated wavefields show qualitative agreement with observations of real sunspots. We use additional numerical experiments to determine, separately, the influence of the thermal structure of the sunspot and the direct effect of the sunspot magnetic field. We use the ray approximation to show that the travel-time shifts in the thermal (non-magnetic) sunspot model are primarily produced by changes in the wave path due to the Wilson depression rather than variations in the wave speed. This shows that inversions for the subsurface structure of sunspots must account for local changes in the density. In some ranges of horizontal phase speed and frequency there is agreement (within the noise level in the simulations) between the travel times measured in the full magnetic sunspot model and the thermal model. If this conclusion proves to be robust for a wide range of models, it would suggest a path towards inversions for sunspot structure.

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Section: Introductionmentioning

confidence: 99%

Helioseismic Holography of Simulated Sunspots: Magnetic and Thermal Contributions to Travel Times

Felipe

Braun

Crouch

et al. 2016

ApJ

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“…It is expected that the theoretical description of acoustic travel times can be improved by accounting for the finite wavelength effects, e.g. by using the Born approximation (Birch & Kosovichev 2000;Birch et al 2004Birch et al , 2011.…”

Section: Resultsmentioning

confidence: 99%

“…The left and right top panels represent maps of the model and reconstructed sound speed perturbations respectively, the bottom left and right panels show vertical and horizontal profiles of the sound-speed perturbation. For comparison, we present inversion results obtained from the same simulation data by Birch et al (2011). They are shown by the dashed curve in the left bottom panel.…”

Section: Resultsmentioning

confidence: 99%

“…Our goal is to examine how well the time-distance measurements and sound-speed inversion results based on acoustic ray-path approximation agree with the travel-time shifts expected from the acoustic ray theory and sound-speed variations of the background model. Similar testing for the travel times measured by the acoustic holography method and soundspeed inversions based on the Born approximation has been published by Birch et al (2011). We introduce the models and numerical simulations in §2.…”

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confidence: 81%

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Verification of the Helioseismology Travel-Time Measurement Technique and the Inversion Procedure for Sound Speed Using Artificial Data

Parchevsky

Zhao

Hartlep

et al. 2014

ApJ

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We performed 3D numerical simulations of the solar surface wave field for the quiet Sun and for three models with different localized sound-speed variations in the interior with: (i) deep, (ii) shallow, and (iii) two-layer structures. We used simulated data generated by two different codes which use the same standard solar model as a background model, but utilize two different integration techniques and use different models of stochastic wave excitation. Acoustic travel times were measured from all data sets using the time-distance helioseismology technique and compared with the ray theory predictions, frequently used for helioseismic travel-time inversions. It is found that the measured travel-time shifts agree well with the ray theory in both cases with and without phasespeed filtering for the shallow and deep perturbations. This testing verifies the whole measuring-filtering-inversion procedure for sound-speed anomalies inside the Sun. It is shown, that the phase-speed filtering, frequently used to improve the signal-to-noise ratio does not introduce significant systematic errors. Results of the sound-speed inversion procedure show good agreement with the background sound-speed profiles in all cases. Due to its smoothing nature, the inversion procedure overestimates sound speed variations in areas with sharp gradients of the sound-speed profile.

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“…Numerical simulations have provided artificial data through which helioseismic analysis and modeling can be tested (Jensen et al, 2003;Benson, Stein, and Nordlund, 2006;Hanasoge et al, 2006;Parchevsky and Kosovichev, 2007;Zhao et al, 2007;Braun et al, 2007;Cameron, Gizon, and Duvall, 2008;Parchevsky and Kosovichev, 2009;Crouch et al, 2010;Cameron et al, 2011;Birch et al, 2011;Hartlep et al, 2011;Braun et al, 2012). Many of these simulations include near-surface flows, sound-speed perturbations, or magnetic structures typical of active regions or supergranulation.…”

Section: Introductionmentioning

confidence: 99%

Helioseismic Holography of an Artificial Submerged Sound Speed Perturbation and Implications for the Detection of Pre-emergence Signatures of Active Regions

Braun¹

2012

Solar Origins of Space Weather and Space Climate

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We use a publicly available numerical wave-propagation simulation of Hartlep et al. (Solar Phys. 268, 321, 2011) to test the ability of helioseismic holography to detect signatures of a compact, fully submerged, 5 % sound-speed perturbation placed at a depth of 50 Mm within a solar model. We find that helioseismic holography as employed in a nominal "lateral-vantage" or "deepfocus" geometry employing quadrants of an annular pupil is capable of detecting and characterizing the perturbation. A number of tests of the methodology, including the use of a plane-parallel approximation, the definition of travel-time shifts, the use of different phase-speed filters, and changes to the pupils, are also performed. It is found that travel-time shifts made using Gabor-wavelet fitting are essentially identical to those derived from the phase of the Fourier transform of the cross-covariance functions. The errors in travel-time shifts caused by the plane-parallel approximation can be minimized to less than a second for the depths and fields of view considered here. Based on the measured strength of the mean travel-time signal of the perturbation, no substantial improvement in sensitivity is produced by varying the analysis procedure from the nominal methodology in conformance with expectations. The measured travel-time shifts are essentially unchanged by varying the profile of the phase-speed filter or omitting the filter entirely. The method remains maximally sensitive when applied with pupils that are wide quadrants, as opposed to narrower quadrants or with pupils composed of smaller arcs. We discuss the significance of these results for the recent controversy regarding suspected pre-emergence signatures of active regions.

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“Hare and Hounds” Tests of Helioseismic Holography

Cited by 11 publications

References 40 publications

Helioseismic Holography of Simulated Sunspots: Magnetic and Thermal Contributions to Travel Times

Helioseismic Holography of Simulated Sunspots: Magnetic and Thermal Contributions to Travel Times

Verification of the Helioseismology Travel-Time Measurement Technique and the Inversion Procedure for Sound Speed Using Artificial Data

Helioseismic Holography of an Artificial Submerged Sound Speed Perturbation and Implications for the Detection of Pre-emergence Signatures of Active Regions

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