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Laurent Gizon - One of the best experts on this subject based on the ideXlab platform.
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Efficient and accurate algorithm for the full modal green's kernel of the scalar wave equation in Helioseismology
SIAM Journal on Applied Mathematics, 2020Co-Authors: Hélène Barucq, Laurent Gizon, Damien Fournier, Florian Faucher, Ha PhamAbstract:In this work, we provide an algorithm to compute efficiently and accurately the full outgoing modal Green's kernel for the scalar wave equation in local Helioseismology under spherical symmetry. Du...
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Probing sunspots with two-skip time–distance Helioseismology
Astronomy & Astrophysics, 2018Co-Authors: Thomas L. Duvall, Paul Stuart Cally, Kaori Nagashima, Damien Przybylski, Laurent GizonAbstract:Context. Previous Helioseismology of sunspots has been sensitive to both the structural and magnetic aspects of sunspot structure. Aims. We aim to develop a technique that is insensitive to the magnetic component so the two aspects can be more readily separated. Methods. We study waves reflected almost vertically from the underside of a sunspot. Time–distance Helioseismology was used to measure travel times for the waves. Ray theory and a detailed sunspot model were used to calculate travel times for comparison. Results. It is shown that these large distance waves are insensitive to the magnetic field in the sunspot. The largest travel time differences for any solar phenomena are observed. Conclusions. With sufficient modeling effort, these should lead to better understanding of sunspot structure.
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probing sunspots with two skip time distance Helioseismology
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Thomas L. Duvall, Paul Stuart Cally, Kaori Nagashima, Damien Przybylski, Laurent GizonAbstract:Previous Helioseismology of sunspots has been sensitive to both the structural and magnetic aspects of sunspot structure. We aim to develop a technique that is insensitive to the magnetic component so the two aspects can be more readily separated. We study waves reflected almost vertically from the underside of a sunspot. Time-distance Helioseismology was used to measure travel times for the waves. Ray theory and a detailed sunspot model were used to calculate travel times for comparison. It is shown that these large distance waves are insensitive to the magnetic field in the sunspot. The largest travel time differences for any solar phenomena are observed. With sufficient modeling effort, these should lead to better understanding of sunspot structure.
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probing sunspots with two skip time distance Helioseismology
Astronomy and Astrophysics, 2018Co-Authors: Thomas L. Duvall, Paul Stuart Cally, Kaori Nagashima, Damien Przybylski, Laurent GizonAbstract:Context. Previous Helioseismology of sunspots has been sensitive to both the structural and magnetic aspects of sunspot structure. Aims. We aim to develop a technique that is insensitive to the magnetic component so the two aspects can be more readily separated. Methods. We study waves reflected almost vertically from the underside of a sunspot. Time–distance Helioseismology was used to measure travel times for the waves. Ray theory and a detailed sunspot model were used to calculate travel times for comparison. Results. It is shown that these large distance waves are insensitive to the magnetic field in the sunspot. The largest travel time differences for any solar phenomena are observed. Conclusions. With sufficient modeling effort, these should lead to better understanding of sunspot structure.
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Problems in computational Helioseismology
arXiv: Solar and Stellar Astrophysics, 2017Co-Authors: Laurent Gizon, Damien Fournier, Thorsten HohageAbstract:We discuss current advances in forward and inverse modeling for local Helioseismology. We report theoretical uniqueness results, in particular the Novikov-Agaltsov reconstruction algorithm, which is relevant to solving the non-linear inverse problem of time-distance Helioseismology (finite amplitude pertubations to the medium). Numerical experiments were conducted to determine the number of frequencies required to reconstruct density and sound speed in the solar interior.
Aaron C. Birch - One of the best experts on this subject based on the ideXlab platform.
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Image compression in local Helioseismology
Astronomy & Astrophysics, 2014Co-Authors: Björn Löptien, Aaron C. Birch, Laurent Gizon, J SchouAbstract:Context. Several upcoming Helioseismology space missions are very limited in telemetry and will have to perform extensive data compression. This requires the development of new methods of data compression. Aims. We give an overview of the influence of lossy data compression on local Helioseismology. We investigate the effects of several lossy compression methods (quantization, JPEG compression, and smoothing and subsampling) on power spectra and time-distance measurements of supergranulation flows at disk center. Methods. We applied different compression methods to tracked and remapped Dopplergrams obtained by the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory. We determined the signal-to-noise ratio of the travel times computed from the compressed data as a function of the compression efficiency. Results. The basic helioseismic measurements that we consider are very robust to lossy data compression. Even if only the sign of the velocity is used, time-distance Helioseismology is still possible. We achieve the best results by applying JPEG compression on spatially subsampled data. However, our conclusions are only valid for supergranulation flows at disk center and may not be valid for all Helioseismology applications.
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Helioseismology with Solar Orbiter
Space Science Reviews, 2014Co-Authors: Björn Löptien, Aaron C. Birch, Laurent Gizon, J Schou, T Appourchaux, Julian Blanco Rodriguez, Paul Stuart Cally, A Gandorfer, Carlos Dominguez-tagle, Frank HillAbstract:The Solar Orbiter mission, to be launched in July 2017, will carry a suite of remote sensing and in-situ instruments, including the Polarimetric and Helioseismic Imager (PHI). PHI will deliver high-cadence images of the Sun in intensity and Doppler velocity suitable for carrying out novel helioseismic studies. The orbit of the Solar Orbiter spacecraft will reach a solar latitude of up to 21∘ (up to 34∘ by the end of the extended mission) and thus will enable the first local Helioseismology studies of the polar regions. Here we consider an array of science objectives to be addressed by Helioseismology within the baseline telemetry allocation (51 Gbit per orbit, current baseline) and within the science observing windows (baseline 3×10 days per orbit). A particularly important objective is the measurement of large-scale flows at high latitudes (rotation and meridional flow), which are largely unknown but play an important role in flux transport dynamos. For both Helioseismology and feature tracking methods convection is a source of noise in the measurement of longitudinally averaged large-scale flows, which decreases as T −1/2 where T is the total duration of the observations. Therefore, the detection of small amplitude signals (e.g., meridional circulation, flows in the deep solar interior) requires long observation times. As an example, one hundred days of observations at lower spatial resolution would provide a noise level of about three m/s on the meridional flow at 80∘ latitude. Longer time-series are also needed to study temporal variations with the solar cycle. The full range of Earth-Sun-spacecraft angles provided by the orbit will enable Helioseismology from two vantage points by combining PHI with another instrument: stereoscopic Helioseismology will allow the study of the deep solar interior and a better understanding of the physics of solar oscillations in both quiet Sun and sunspots. We have used a model of the PHI instrument to study its performance for Helioseismology applications. As input we used a 6 hr time-series of realistic solar magneto-convection simulation (Stagger code) and the SPINOR radiative transfer code to synthesize the observables. The simulated power spectra of solar oscillations show that the instrument is suitable for Helioseismology. In particular, the specified point spread function, image jitter, and photon noise are no obstacle to a successful mission.
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Multi-Channel Three-Dimensional SOLA Inversion for Local Helioseismology
Solar Physics, 2011Co-Authors: Jason Jackiewicz, Aaron C. Birch, Laurent Gizon, Thorsten Hohage, Shravan M. Hanasoge, Jean-baptiste Ruffio, Michal ŠvandaAbstract:Inversions for local Helioseismology are an important and necessary step for obtaining three-dimensional maps of various physical quantities in the solar interior. Frequently, the full inverse problems that one would like to solve prove intractable because of computational constraints. Due to the enormous seismic data sets that already exist and those forthcoming, this is a problem that needs to be addressed. To this end, we present a very efficient linear inversion algorithm for local Helioseismology. It is based on a subtractive optimally localized averaging (SOLA) scheme in the Fourier domain, utilizing the horizontal-translation invariance of the sensitivity kernels. In Fourier space the problem decouples into many small problems, one for each horizontal wave vector. This multi-channel SOLA method is demonstrated for an example problem in time-distance Helioseismology that is small enough to be solved both in real and Fourier space. We find that both approaches are successful in solving the inverse problem. However, the multi-channel SOLA algorithm is much faster and can easily be parallelized.
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Progress in sunspot Helioseismology
Journal of Physics: Conference Series, 2011Co-Authors: Aaron C. BirchAbstract:Local Helioseismology is a set of methods that are used to study wave propagation and infer physical conditions in the solar interior. Sunspots are a particularly challenging target for local Helioseismology. In this review, I will show that some new methods (magnetoconvection simulations and numerical wave propagation simulations) lead to shallow sunspot models that are apparently inconsistent with traditional inferences from local Helioseismology. In addition, I will show that inferences for the depth structure of moat flows are not in general agreement either.
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Local Helioseismology: Three Dimensional Imaging of the Solar Interior
Annual Review of Astronomy and Astrophysics, 2010Co-Authors: Laurent Gizon, Aaron C. Birch, Hendrik C. SpruitAbstract:The Sun supports a rich spectrum of internal waves that are continuously excited by turbulent convection. The GONG network and the MDI/SOHO space instrument provide an exceptional data base of spatially-resolved observations of solar oscillations, covering an entire sunspot cycle (11 years). Local Helioseismology is a set of tools for probing the solar interior in three dimensions using measurements of wave travel times and local mode frequencies. Local Helioseismology has discovered (i) near-surface vector flows associated with convection (ii) 250 m/s subsurface horizontal outflows around sunspots (iii) ~50 m/s extended horizontal flows around active regions (converging near the surface and diverging below), (iv) the effect of the Coriolis force on convective flows and active region flows (v) the subsurface signature of the 15 m/s poleward meridional flow, (vi) a +/-5 m/s time-varying depth-dependent component of the meridional circulation around the mean latitude of activity, and (vii) magnetic activity on the far side of the Sun.
Sarbani Basu - One of the best experts on this subject based on the ideXlab platform.
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Global seismology of the Sun
Living Reviews in Solar Physics, 2016Co-Authors: Sarbani BasuAbstract:The seismic study of the Sun and other stars offers a unique window into the interior of these stars. Thanks to Helioseismology, we know the structure of the Sun to admirable precision. In fact, our knowledge is good enough to use the Sun as a laboratory. We have also been able to study the dynamics of the Sun in great detail. Helioseismic data also allow us to probe the changes that take place in the Sun as solar activity waxes and wanes. The seismic study of stars other than the Sun is a fairly new endeavour, but we are making great strides in this field. In this review I discuss some of the techniques used in helioseismic analyses and the results obtained using those techniques. I focus on results obtained with global Helioseismology, i.e., the study of the Sun using its normal modes of oscillation. I also briefly touch upon asteroseismology, the seismic study of stars other than the Sun, and discuss how seismic data of others stars are interpreted.
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Local Helioseismology of sunspot regions: comparison of ring-diagram and time-distance results
Journal of Physics: Conference Series, 2011Co-Authors: Alexander G. Kosovichev, Sarbani Basu, Thomas Hartlep, R. Howe, R. S. Bogart, Thomas L. Duvall, I. Gonzalez-hernandez, Deborah A. Haber, Rudolf Komm, Shukur KholikovAbstract:Local Helioseismology provides unique information about the subsurface structure and dynamics of sunspots and active regions. However, because of complexity of sunspot regions local Helioseismology diagnostics require careful analysis of systematic uncertainties and physical interpretation of the inversion results. We present new results of comparison of the ring-diagram analysis and time-distance Helioseismology for active region NOAA 9787, for which a previous comparison showed significant differences in the subsurface sound-speed structure, and discuss systematic uncertainties of the measurements and inversions. Our results show that both the ring-diagram and time-distance techniques give qualitatively similar results, revealing a characteristic two-layer seismic sound-speed structure consistent with the results for other active regions. However, a quantitative comparison of the inversion results is not straightforward. It must take into account differences in the sensitivity, spatial resolution and the averaging kernels. In particular, because of the acoustic power suppression, the contribution of the sunspot seismic structure to the ring-diagram signal can be substantially reduced. We show that taking into account this effect reduces the difference in the depth of transition between the negative and positive sound-speed variations inferred by these methods. Further detailed analysis of the sensitivity, resolution and averaging properties of the local Helioseismology methods is necessary for consolidation of the inversion results. It seems to be important that both methods indicate that the seismic structure of sunspots is rather deep and extends to at least 20 Mm below the surface, putting constraints on theoretical models of sunspots.
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Helioseismology as a diagnostic of the solar interior
Astrophysics and Space Science, 2009Co-Authors: Sarbani BasuAbstract:Helioseismology has given us a unique window into the solar interior. Helioseismic data have enabled us to study the internal structure and dynamics with unprecedented detail. This has also allowed us to use the Sun as a laboratory to study the basic properties of stellar matter. We describe how Helioseismology is used to determine solar structure and what we have learned about the Sun so far. We also describe how knowledge of the solar structure can be used to constrain the physics inputs.
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Perspectives in Global Helioseismology and the Road Ahead
Solar Physics, 2008Co-Authors: William J. Chaplin, Sarbani BasuAbstract:We review the impact of global Helioseismology on key questions concerning the internal structure and dynamics of the Sun and consider the exciting challenges the field faces as it enters a fourth decade of science exploitation. We do so with an eye on the past, looking at the perspectives global Helioseismology offered in its earlier phases, in particular the mid-to-late 1970s and the 1980s. We look at how modern, higher quality, longer datasets coupled with new developments in analysis have altered, refined, and changed some of those perspectives and opened others that were not previously available for study. We finish by discussing outstanding challenges and questions for the field.
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Helioseismology and solar abundances
Physics Reports, 2008Co-Authors: Sarbani Basu, H. M. AntiaAbstract:Helioseismology has allowed us to study the structure of the Sun in unprecedented detail. One of the triumphs of the theory of stellar evolution was that helioseismic studies had shown that the structure of solar models is very similar to that of the Sun. However, this agreement has been spoiled by recent revisions of the solar heavy-element abundances. Heavy-element abundances determine the opacity of the stellar material and hence, are an important input to stellar model calculations. The models with the new, low abundances do not satisfy helioseismic constraints. We review here how heavy-element abundances affect solar models, how these models are tested with Helioseismology, and the impact of the new abundances on standard solar models. We also discuss the attempts made to improve the agreement of the low-abundance models with the Sun and discuss how Helioseismology is being used to determine the solar heavy-element abundances. A review of current literature shows that attempts to improve agreement between solar models with low heavy-element abundances and seismic inference have been unsuccessful so far. The low-metallicity models that have the least disagreement with seismic data require changing all input physics to stellar models beyond their acceptable ranges. Seismic determinations of the solar heavy-element abundances yield results that are consistent with the older, higher values of the solar abundance, and hence, no major changes to the inputs to solar models are required to make higher-metallicity solar models consistent with the helioseismic data.
Alexander G. Kosovichev - One of the best experts on this subject based on the ideXlab platform.
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Reconstruction of Solar Subsurfaces by Local Helioseismology
Cartography of the Sun and the Stars, 2016Co-Authors: Alexander G. Kosovichev, Junwei ZhaoAbstract:Local Helioseismology has opened new frontiers in our quest for understanding of the internal dynamics and dynamo on the Sun. Local Helioseismology reconstructs subsurface structures and flows by extracting coherent signals of acoustic waves traveling through the interior and carrying information about subsurface perturbations and flows, from stochastic oscillations observed on the surface. The initial analysis of the subsurface flow maps reconstructed from the 5 years of SDO/HMI data by time-distance Helioseismology reveals the great potential for studying and understanding of the dynamics of the quiet Sun and active regions, and the evolution with the solar cycle. In particular, our results show that the emergence and evolution of active regions are accompanied by multi-scale flow patterns, and that the meridional flows display the North-South asymmetry closely correlating with the magnetic activity. The latitudinal variations of the meridional circulation speed, which are probably related to the large-scale converging flows, are mostly confined in shallow subsurface layers. Therefore, these variations do not necessarily affect the magnetic flux transport. The North-South asymmetry is also pronounced in the variations of the differential rotation (‘torsional oscillations’). The calculations of a proxy of the subsurface kinetic helicity density show that the helicity does not vary during the solar cycle, and that supergranulation is a likely source of the near-surface helicity.
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Local Helioseismology of Sunspots: Current Status and Perspectives
Solar Physics, 2012Co-Authors: Alexander G. KosovichevAbstract:Mechanisms of the formation and stability of sunspots are among the longest-standing and intriguing puzzles of solar physics and astrophysics. Sunspots are controlled by subsurface dynamics, hidden from direct observations. Recently, substantial progress in our understanding of the physics of the turbulent magnetized plasma in strong-field regions has been made by using numerical simulations and local Helioseismology. Both the simulations and helioseismic measurements are extremely challenging, but it is becoming clear that the key to understanding the enigma of sunspots is a synergy between models and observations. Recent observations and radiative MHD numerical models have provided a convincing explanation for the Evershed flows in sunspot penumbrae. Also, they lead to the understanding of sunspots as self-organized magnetic structures in the turbulent plasma of the upper convection zone, which are maintained by a large-scale dynamics. Local helioseismic diagnostics of sunspots still have many uncertainties, some of which are discussed in this review. However, there have been significant achievements in resolving these uncertainties, verifying the basic results by new high-resolution observations, testing the helioseismic techniques by numerical simulations, and comparing results obtained by different methods. For instance, a recent analysis of Helioseismology data from the Hinode space mission has successfully resolved several uncertainties and concerns (such as the inclined-field and phase-speed filtering effects) that might affect the inferences of the subsurface wave-speed structure of sunspots and the flow pattern. It is becoming clear that for the understanding of the phenomenon of sunspots it is important to further improve the Helioseismology methods and investigate the whole life cycle of active regions, from magnetic flux emergence to dissipation. The Solar Dynamics Observatory mission has started to provide data for such investigations.
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Dark Matter and its Effects on Helioseismology
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Ryan Hamerly, Alexander G. KosovichevAbstract:Helioseismology can be used to place new constraints on the properties of dark matter, allowing solar observations to complement more conventional dark matter searches currently in operation. During the course of its lifetime, the Sun accretes a sizeable amount of dark matter. This accreted matter affects the heat transport of the stellar core in ways that Helioseismology can detect, or at least constrain. We modify the CESAM stellar evolution code to take account of dark matter and determine the effect of WIMP models on the stellar structure and normal-mode oscillation frequencies.
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Advances in Global and Local Helioseismology: An Introductory Review
The Pulsations of the Sun and the Stars, 2011Co-Authors: Alexander G. KosovichevAbstract:Helioseismology studies the structure and dynamics of the Sun’s interior by observing oscillations on the surface. These studies provide information about the physical processes that control the evolution and magnetic activity of the Sun. In recent years, Helioseismology has made substantial progress towards the understanding of the physics of solar oscillations and the physical processes inside the Sun, thanks to observational, theoretical and modeling efforts. In addition to global seismology of the Sun based on measurements of global oscillation modes, a new field of local Helioseismology, which studies oscillation travel times and local frequency shifts, has been developed. It is capable of providing 3D images of subsurface structures and flows. The basic principles, recent advances and perspectives of global and local Helioseismology are reviewed in this article.
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Local Helioseismology of sunspot regions: comparison of ring-diagram and time-distance results
Journal of Physics: Conference Series, 2011Co-Authors: Alexander G. Kosovichev, Sarbani Basu, Thomas Hartlep, R. Howe, R. S. Bogart, Thomas L. Duvall, I. Gonzalez-hernandez, Deborah A. Haber, Rudolf Komm, Shukur KholikovAbstract:Local Helioseismology provides unique information about the subsurface structure and dynamics of sunspots and active regions. However, because of complexity of sunspot regions local Helioseismology diagnostics require careful analysis of systematic uncertainties and physical interpretation of the inversion results. We present new results of comparison of the ring-diagram analysis and time-distance Helioseismology for active region NOAA 9787, for which a previous comparison showed significant differences in the subsurface sound-speed structure, and discuss systematic uncertainties of the measurements and inversions. Our results show that both the ring-diagram and time-distance techniques give qualitatively similar results, revealing a characteristic two-layer seismic sound-speed structure consistent with the results for other active regions. However, a quantitative comparison of the inversion results is not straightforward. It must take into account differences in the sensitivity, spatial resolution and the averaging kernels. In particular, because of the acoustic power suppression, the contribution of the sunspot seismic structure to the ring-diagram signal can be substantially reduced. We show that taking into account this effect reduces the difference in the depth of transition between the negative and positive sound-speed variations inferred by these methods. Further detailed analysis of the sensitivity, resolution and averaging properties of the local Helioseismology methods is necessary for consolidation of the inversion results. It seems to be important that both methods indicate that the seismic structure of sunspots is rather deep and extends to at least 20 Mm below the surface, putting constraints on theoretical models of sunspots.
Thomas L. Duvall - One of the best experts on this subject based on the ideXlab platform.
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probing sunspots with two skip time distance Helioseismology
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Thomas L. Duvall, Paul Stuart Cally, Kaori Nagashima, Damien Przybylski, Laurent GizonAbstract:Previous Helioseismology of sunspots has been sensitive to both the structural and magnetic aspects of sunspot structure. We aim to develop a technique that is insensitive to the magnetic component so the two aspects can be more readily separated. We study waves reflected almost vertically from the underside of a sunspot. Time-distance Helioseismology was used to measure travel times for the waves. Ray theory and a detailed sunspot model were used to calculate travel times for comparison. It is shown that these large distance waves are insensitive to the magnetic field in the sunspot. The largest travel time differences for any solar phenomena are observed. With sufficient modeling effort, these should lead to better understanding of sunspot structure.
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Probing sunspots with two-skip time–distance Helioseismology
Astronomy & Astrophysics, 2018Co-Authors: Thomas L. Duvall, Paul Stuart Cally, Kaori Nagashima, Damien Przybylski, Laurent GizonAbstract:Context. Previous Helioseismology of sunspots has been sensitive to both the structural and magnetic aspects of sunspot structure. Aims. We aim to develop a technique that is insensitive to the magnetic component so the two aspects can be more readily separated. Methods. We study waves reflected almost vertically from the underside of a sunspot. Time–distance Helioseismology was used to measure travel times for the waves. Ray theory and a detailed sunspot model were used to calculate travel times for comparison. Results. It is shown that these large distance waves are insensitive to the magnetic field in the sunspot. The largest travel time differences for any solar phenomena are observed. Conclusions. With sufficient modeling effort, these should lead to better understanding of sunspot structure.
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probing sunspots with two skip time distance Helioseismology
Astronomy and Astrophysics, 2018Co-Authors: Thomas L. Duvall, Paul Stuart Cally, Kaori Nagashima, Damien Przybylski, Laurent GizonAbstract:Context. Previous Helioseismology of sunspots has been sensitive to both the structural and magnetic aspects of sunspot structure. Aims. We aim to develop a technique that is insensitive to the magnetic component so the two aspects can be more readily separated. Methods. We study waves reflected almost vertically from the underside of a sunspot. Time–distance Helioseismology was used to measure travel times for the waves. Ray theory and a detailed sunspot model were used to calculate travel times for comparison. Results. It is shown that these large distance waves are insensitive to the magnetic field in the sunspot. The largest travel time differences for any solar phenomena are observed. Conclusions. With sufficient modeling effort, these should lead to better understanding of sunspot structure.
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Local Helioseismology of sunspot regions: comparison of ring-diagram and time-distance results
Journal of Physics: Conference Series, 2011Co-Authors: Alexander G. Kosovichev, Sarbani Basu, Thomas Hartlep, R. Howe, R. S. Bogart, Thomas L. Duvall, I. Gonzalez-hernandez, Deborah A. Haber, Rudolf Komm, Shukur KholikovAbstract:Local Helioseismology provides unique information about the subsurface structure and dynamics of sunspots and active regions. However, because of complexity of sunspot regions local Helioseismology diagnostics require careful analysis of systematic uncertainties and physical interpretation of the inversion results. We present new results of comparison of the ring-diagram analysis and time-distance Helioseismology for active region NOAA 9787, for which a previous comparison showed significant differences in the subsurface sound-speed structure, and discuss systematic uncertainties of the measurements and inversions. Our results show that both the ring-diagram and time-distance techniques give qualitatively similar results, revealing a characteristic two-layer seismic sound-speed structure consistent with the results for other active regions. However, a quantitative comparison of the inversion results is not straightforward. It must take into account differences in the sensitivity, spatial resolution and the averaging kernels. In particular, because of the acoustic power suppression, the contribution of the sunspot seismic structure to the ring-diagram signal can be substantially reduced. We show that taking into account this effect reduces the difference in the depth of transition between the negative and positive sound-speed variations inferred by these methods. Further detailed analysis of the sensitivity, resolution and averaging properties of the local Helioseismology methods is necessary for consolidation of the inversion results. It seems to be important that both methods indicate that the seismic structure of sunspots is rather deep and extends to at least 20 Mm below the surface, putting constraints on theoretical models of sunspots.
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Validation of Helioseismology through Forward Modeling: Realization Noise Subtraction and Kernels
The Astrophysical Journal, 2007Co-Authors: Shravan M. Hanasoge, Thomas L. Duvall, Sebastien CouvidatAbstract:Through a series of numerical simulations of the near-surface acoustic wavefield of the Sun, we show the utility of the forward approach in local Helioseismology. We demonstrate and apply a method to subtract a large fraction of the realization noise from the simulated data. The ability to attain high signal-to-noise ratios from brief forward calculations implies that computational resources are less of a bottleneck, making this alternate method for investigations of the solar interior very feasible. We put this method to use by deriving sensitivity kernels for sound-speed perturbations and source suppression for the background state in our computations using techniques of time-distance Helioseismology, all from merely 48 hr of artificial data.
