Duvall, Thomas L.

[["dc.bibliographiccitation.artnumber","A9"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","587"],["dc.contributor.author","Löptien, Björn"],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Duvall, Thomas L."],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Schou, J."],["dc.date.accessioned","2017-09-07T11:49:58Z"],["dc.date.available","2017-09-07T11:49:58Z"],["dc.date.issued","2016"],["dc.description.abstract","Context. Several upcoming and proposed space missions, such as Solar Orbiter, will be limited in telemetry and thus require data compression.Aims. We test the impact of data compression on local correlation tracking (LCT) of time series of continuum intensity images. We evaluate the effect of several lossy compression methods (quantization, JPEG compression, and a reduced number of continuum images) on measurements of solar differential rotation with LCT.Methods. We applied the different compression methods to tracked and remapped continuum intensity maps obtained by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. We derived 2D vector velocities using the local correlation tracking code Fourier Local Correlation Tracking (FLCT) and determined the additional bias and noise introduced by compression to differential rotation.Results. We find that probing differential rotation with LCT is very robust to lossy data compression when using quantization. Our results are severely affected by systematic errors of the LCT method and the HMI instrument. The sensitivity of LCT to systematic errors is a concern for Solar Orbiter."],["dc.identifier.doi","10.1051/0004-6361/201526805"],["dc.identifier.gro","3147451"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/13430"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5015"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/ 312844"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/ 312495"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Data compression for local correlation tracking of solar granulation"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","553"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","The Astrophysical Journal"],["dc.bibliographiccitation.lastpage","559"],["dc.bibliographiccitation.volume","646"],["dc.contributor.author","Duvall, Thomas L."],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Gizon, Laurent"],["dc.date.accessioned","2017-09-07T11:49:44Z"],["dc.date.available","2017-09-07T11:49:44Z"],["dc.date.issued","2006"],["dc.description.abstract","American Astronomical Society logo American Astronomical Society logo iop-2016.png iop-2016.png A publishing partnership Direct Measurement of Travel-Time Kernels for Helioseismology T. L. Duvall, Jr.1, A. C. Birch2, and L. Gizon3 © 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A. The Astrophysical Journal, Volume 646, Number 1 Download Article PDF View article References 391 Total downloads 36 36 total citations on Dimensions. Turn on MathJax Get permission to re-use this article Share this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on CiteULike Share on Mendeley Article information Abstract Solar f-modes are surface gravity waves that propagate horizontally in a thin layer near the photosphere with a dispersion relation approximately that of deep water waves. At the power maximum near frequency ω/2π = 3 mHz, the wavelength of 5 Mm is large enough for various wave scattering properties to be observable. Gizon & Birch have calculated spatial kernels for scattering in the Born approximation. In this paper, using isolated small magnetic features as approximate point scatterers, a linear-response kernel has been measured. In addition, the kernel has been estimated by deconvolving the magnetograms from the travel-time maps. The observed kernel is similar to the theoretical kernel for wave damping computed by Gizon & Birch: it includes elliptical and hyperbolic features. This is the first observational evidence to suggest that it is appropriate to use the Born approximation to compute kernels (as opposed to the ray approximation). Furthermore, the observed hyperbolic features confirm that it is important to take into account scattering of the waves coming from distant source locations (as opposed to the single-source approximation). The observed kernel is due to a superposition of the direct and indirect effects of the magnetic field. A simple model that includes both monopole and dipole scattering compares favorably with the data. This new technique appears to be promising to study how seismic waves interact with magnetic flux tubes."],["dc.identifier.doi","10.1086/504792"],["dc.identifier.gro","3147418"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5004"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","0004-637X"],["dc.title","Direct Measurement of Travel‐Time Kernels for Helioseismology"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dc.type.peerReviewed","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A59"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","649"],["dc.contributor.author","Böning, Vincent G. A."],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Duvall, Thomas L."],["dc.date.accessioned","2021-07-05T15:00:35Z"],["dc.date.available","2021-07-05T15:00:35Z"],["dc.date.issued","2021"],["dc.description.abstract","Context. Understanding convection is important in stellar physics, for example, when it is an input in stellar evolution models. Helioseismic estimates of convective flow amplitudes in deeper regions of the solar interior disagree by orders of magnitude among themselves and with simulations. Aims. We aim to assess the validity of an existing upper limit of solar convective flow amplitudes at a depth of 0.96 solar radii obtained using time-distance helioseismology and several simplifying assumptions. Methods. We generated synthetic observations for convective flow fields from a magnetohydrodynamic simulation (MURaM) using travel-time sensitivity functions and a noise model. We compared the estimates of the flow amplitude with the actual value of the flow. Results. For the scales of interest ( ℓ  < 100), we find that the current procedure for obtaining an upper limit gives the correct order of magnitude of the flow for the given flow fields. We also show that this estimate is not an upper limit in a strict sense because it underestimates the flow amplitude at the largest scales by a factor of about two because the scale dependence of the signal-to-noise ratio has to be taken into account. After correcting for this and after taking the dependence of the measurements on direction in Fourier space into account, we show that the obtained estimate is indeed an upper limit. Conclusions. We conclude that time-distance helioseismology is able to correctly estimate the order of magnitude (or an upper limit) of solar convective flows in the deeper interior when the vertical correlation function of the different flow components is known and the scale dependence of the signal-to-noise ratio is taken into account. We suggest that future work should include information from different target depths to better separate the effect of near-surface flows from those at greater depths. In addition, the measurements are sensitive to all three flow directions, which should be taken into account."],["dc.description.abstract","Context. Understanding convection is important in stellar physics, for example, when it is an input in stellar evolution models. Helioseismic estimates of convective flow amplitudes in deeper regions of the solar interior disagree by orders of magnitude among themselves and with simulations. Aims. We aim to assess the validity of an existing upper limit of solar convective flow amplitudes at a depth of 0.96 solar radii obtained using time-distance helioseismology and several simplifying assumptions. Methods. We generated synthetic observations for convective flow fields from a magnetohydrodynamic simulation (MURaM) using travel-time sensitivity functions and a noise model. We compared the estimates of the flow amplitude with the actual value of the flow. Results. For the scales of interest ( ℓ  < 100), we find that the current procedure for obtaining an upper limit gives the correct order of magnitude of the flow for the given flow fields. We also show that this estimate is not an upper limit in a strict sense because it underestimates the flow amplitude at the largest scales by a factor of about two because the scale dependence of the signal-to-noise ratio has to be taken into account. After correcting for this and after taking the dependence of the measurements on direction in Fourier space into account, we show that the obtained estimate is indeed an upper limit. Conclusions. We conclude that time-distance helioseismology is able to correctly estimate the order of magnitude (or an upper limit) of solar convective flows in the deeper interior when the vertical correlation function of the different flow components is known and the scale dependence of the signal-to-noise ratio is taken into account. We suggest that future work should include information from different target depths to better separate the effect of near-surface flows from those at greater depths. In addition, the measurements are sensitive to all three flow directions, which should be taken into account."],["dc.identifier.doi","10.1051/0004-6361/202039311"],["dc.identifier.pii","aa39311-20"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/87860"],["dc.notes.intern","DOI Import DOI-Import GROB-441"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Helioseismological determination of the subsurface spatial spectrum of solar convection: Demonstration using numerical simulations"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A181"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","635"],["dc.contributor.author","Böning, Vincent G. A."],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Duvall, Thomas L."],["dc.contributor.author","Schou, Jesper"],["dc.date.accessioned","2020-12-10T18:11:55Z"],["dc.date.available","2020-12-10T18:11:55Z"],["dc.date.issued","2020"],["dc.identifier.doi","10.1051/0004-6361/201937331"],["dc.identifier.eissn","1432-0746"],["dc.identifier.issn","0004-6361"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/74186"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","Characterizing the spatial pattern of solar supergranulation using the bispectrum"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A99"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","619"],["dc.contributor.author","Liang, Zhi-Chao"],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Duvall, Thomas L."],["dc.contributor.author","Rajaguru, S. P."],["dc.date.accessioned","2020-12-10T18:11:43Z"],["dc.date.available","2020-12-10T18:11:43Z"],["dc.date.issued","2018"],["dc.identifier.doi","10.1051/0004-6361/201833673"],["dc.identifier.eissn","1432-0746"],["dc.identifier.issn","0004-6361"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/74116"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","Solar meridional circulation from twenty-one years of SOHO/MDI and SDO/HMI observations"],["dc.title.alternative","Helioseismic travel times and forward modeling in the ray approximation"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","568"],["dc.bibliographiccitation.issue","7"],["dc.bibliographiccitation.journal","Nature Astronomy"],["dc.bibliographiccitation.lastpage","573"],["dc.bibliographiccitation.volume","2"],["dc.contributor.author","Löptien, Björn"],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Schou, Jesper"],["dc.contributor.author","Proxauf, Bastian"],["dc.contributor.author","Duvall, Thomas L."],["dc.contributor.author","Bogart, Richard S."],["dc.contributor.author","Christensen, Ulrich R."],["dc.date.accessioned","2020-05-18T14:29:12Z"],["dc.date.available","2020-05-18T14:29:12Z"],["dc.date.issued","2018"],["dc.identifier.doi","10.1038/s41550-018-0460-x"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/65540"],["dc.relation.issn","2397-3366"],["dc.title","Global-scale equatorial Rossby waves as an essential component of solar internal dynamics"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","626"],["dc.contributor.author","Liang, Zhi-Chao"],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Duvall, Thomas L."],["dc.date.accessioned","2020-12-10T18:11:46Z"],["dc.date.available","2020-12-10T18:11:46Z"],["dc.date.issued","2019"],["dc.identifier.doi","10.1051/0004-6361/201834849"],["dc.identifier.eissn","1432-0746"],["dc.identifier.issn","0004-6361"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/74138"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","Time-distance helioseismology of solar Rossby waves"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","257"],["dc.bibliographiccitation.issue","1-4"],["dc.bibliographiccitation.journal","Space Science Reviews"],["dc.bibliographiccitation.lastpage","258"],["dc.bibliographiccitation.volume","156"],["dc.contributor.author","Gizon, L."],["dc.contributor.author","Schunker, H."],["dc.contributor.author","Baldner, C. S."],["dc.contributor.author","Basu, S."],["dc.contributor.author","Birch, A. C."],["dc.contributor.author","Bogart, R. S."],["dc.contributor.author","Braun, D. C."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Duvall Jr., T. L."],["dc.contributor.author","Hanasoge, S. M."],["dc.contributor.author","Jackiewicz, J."],["dc.contributor.author","Roth, M."],["dc.contributor.author","Stahn, T."],["dc.contributor.author","Thompson, M. J."],["dc.contributor.author","Zharkov, S."],["dc.date.accessioned","2017-09-07T11:48:39Z"],["dc.date.available","2017-09-07T11:48:39Z"],["dc.date.issued","2010"],["dc.identifier.doi","10.1007/s11214-010-9688-1"],["dc.identifier.gro","3146992"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/4741"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.eissn","1572-9672"],["dc.relation.iserratumof","/handle/2/4740"],["dc.relation.issn","0038-6308"],["dc.title","Erratum to: Helioseismology of Sunspots: A Case Study of NOAA Region 9787"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","erratum_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A103"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","644"],["dc.contributor.author","Hanson, Chris S."],["dc.contributor.author","Duvall, Thomas L."],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Sreenivasan, Katepalli R."],["dc.date.accessioned","2021-03-05T08:58:40Z"],["dc.date.available","2021-03-05T08:58:40Z"],["dc.date.issued","2020"],["dc.identifier.doi","10.1051/0004-6361/202039108"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/80205"],["dc.notes.intern","DOI Import GROB-393"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Solar east-west flow correlations that persist for months at low latitudes are dominated by active region inflows"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A130"],["dc.bibliographiccitation.firstpage","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","8"],["dc.bibliographiccitation.volume","590"],["dc.contributor.author","Löptien, B."],["dc.contributor.author","Birch, A. C."],["dc.contributor.author","Duvall Jr., T. L."],["dc.contributor.author","Gizon, L."],["dc.contributor.author","Schou, J."],["dc.date.accessioned","2017-09-07T11:48:41Z"],["dc.date.available","2017-09-07T11:48:41Z"],["dc.date.issued","2016"],["dc.description.abstract","Context. Local correlation tracking of granulation (LCT) is an important method for measuring horizontal flows in the photosphere. This method exhibits a systematic error that looks like a flow converging toward disk center, which is also known as the shrinking-Sun effect. Aims. We aim to study the nature of the shrinking-Sun effect for continuum intensity data and to derive a simple model that can explain its origin. Methods. We derived LCT flow maps by running the LCT code Fourier Local Correlation Tracking (FLCT) on tracked and remapped continuum intensity maps provided by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We also computed flow maps from synthetic continuum images generated from STAGGER code simulations of solar surface convection. We investigated the origin of the shrinking-Sun effect by generating an average granule from synthetic data from the simulations. Results. The LCT flow maps derived from the HMI data and the simulations exhibit a shrinking-Sun effect of comparable magnitude. The origin of this effect is related to the apparent asymmetry of granulation originating from radiative transfer effects when observing with a viewing angle inclined from vertical. This causes, in combination with the expansion of the granules, an apparent motion toward disk center."],["dc.identifier.doi","10.1051/0004-6361/201628112"],["dc.identifier.gro","3147015"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/14286"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/4758"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/312844/EU/Exploitation of Space Data for Innovative Helio- and Asteroseismology/SPACEINN"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/312495/EU/High-Resolution Solar Physics Network/SOLARNET"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","The shrinking Sun: A systematic error in local correlation tracking of solar granulation"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]