Cameron, Robert H.

[["dc.bibliographiccitation.firstpage","A183"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","664"],["dc.contributor.author","Baumgartner, C."],["dc.contributor.author","Birch, A. C."],["dc.contributor.author","Schunker, H."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Gizon, L."],["dc.date.accessioned","2022-10-04T10:22:20Z"],["dc.date.available","2022-10-04T10:22:20Z"],["dc.date.issued","2022"],["dc.description.abstract","Context.\n The twist of the magnetic field above a sunspot is an important quantity in solar physics. For example, magnetic twist plays a role in the initiation of flares and coronal mass ejections (CMEs). Various proxies for the twist above the photosphere have been found using models of uniformly twisted flux tubes, and are routinely computed from single photospheric vector magnetograms. One class of proxies is based on\n α\n \n z\n \n , the ratio of the vertical current to the vertical magnetic field. Another class of proxies is based on the so-called twist density,\n q\n , which depends on the ratio of the azimuthal field to the vertical field. However, the sensitivity of these proxies to temporal fluctuations of the magnetic field has not yet been well characterized.\n \n \n Aims.\n We aim to determine the sensitivity of twist proxies to temporal fluctuations in the magnetic field as estimated from time-series of SDO/HMI vector magnetic field maps.\n \n \n Methods.\n To this end, we introduce a model of a sunspot with a peak vertical field of 2370 Gauss at the photosphere and a uniform twist density\n q\n  = −0.024 Mm\n −1\n . We add realizations of the temporal fluctuations of the magnetic field that are consistent with SDO/HMI observations, including the spatial correlations. Using a Monte-Carlo approach, we determine the robustness of the different proxies to the temporal fluctuations.\n \n \n Results.\n The temporal fluctuations of the three components of the magnetic field are correlated for spatial separations up to 1.4 Mm (more than expected from the point spread function alone). The Monte-Carlo approach enables us to demonstrate that several proxies for the twist of the magnetic field are not biased in each of the individual magnetograms. The associated random errors on the proxies have standard deviations in the range between 0.002 and 0.006 Mm\n −1\n , which is smaller by approximately one order of magnitude than the mean value of\n q\n ."],["dc.identifier.doi","10.1051/0004-6361/202243357"],["dc.identifier.pii","aa43357-22"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/114646"],["dc.notes.intern","DOI-Import GROB-600"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Impact of spatially correlated fluctuations in sunspots on metrics related to magnetic twist"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","8"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","The Astrophysical Journal Supplement Series"],["dc.bibliographiccitation.volume","229"],["dc.contributor.author","Jafarzadeh, S."],["dc.contributor.author","Solanki, Parth K."],["dc.contributor.author","Cameron, Robert H."],["dc.contributor.author","Barthol, P."],["dc.contributor.author","Blanco Rodriguez, J."],["dc.contributor.author","del Toro Iniesta, J. C."],["dc.contributor.author","Gandorfer, A."],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Hirzberger, J."],["dc.contributor.author","Knoelker, M."],["dc.contributor.author","Pillet, V. Martinez"],["dc.contributor.author","Orozco Suarez, D."],["dc.contributor.author","Riethmueller, T. L."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","van Noort, M."],["dc.date.accessioned","2018-11-07T10:26:55Z"],["dc.date.available","2018-11-07T10:26:55Z"],["dc.date.issued","2017"],["dc.description.abstract","Convective flows are known as the prime means of transporting magnetic fields on the solar surface. Thus, small magnetic structures are good tracers of turbulent flows. We study the migration and dispersal of magnetic bright features (MBFs) in intergranular areas observed at high spatial resolution with SUNRISE/IMaX. We describe the flux dispersal of individual MBFs as a diffusion process whose parameters are computed for various areas in the quiet-Sun and the vicinity of active regions from seeing-free data. We find that magnetic concentrations are best described as random walkers close to network areas (diffusion index, gamma = 1.0), travelers with constant speeds over a supergranule (gamma = 1.9-2.0), and decelerating movers in the vicinity of flux emergence and/or within active regions (gamma = 1.4-1.5). The three types of regions host MBFs with mean diffusion coefficients of 130 km(2) s(-1), 80-90 km(2) s(-1), and 25-70 km(2) s(-1), respectively. The MBFs in these three types of regions are found to display a distinct kinematic behavior at a confidence level in excess of 95%."],["dc.identifier.doi","10.3847/1538-4365/229/1/8"],["dc.identifier.isi","000397557300008"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/43141"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","PUB_WoS_Import"],["dc.publisher","Iop Publishing Ltd"],["dc.relation.issn","1538-4365"],["dc.relation.issn","0067-0049"],["dc.title","Kinematics of Magnetic Bright Features in the Solar Photosphere"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","L23"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","The Astrophysical Journal Letters"],["dc.bibliographiccitation.volume","934"],["dc.contributor.affiliation","Nèmec, N.-E.;"],["dc.contributor.affiliation","Shapiro, A. I.;"],["dc.contributor.affiliation","Işık, E.;"],["dc.contributor.affiliation","Sowmya, K.;"],["dc.contributor.affiliation","Solanki, S. K.;"],["dc.contributor.affiliation","Krivova, N. A.;"],["dc.contributor.affiliation","Cameron, R. H.;"],["dc.contributor.affiliation","Gizon, L.;"],["dc.contributor.author","Nèmec, N.-E."],["dc.contributor.author","Shapiro, A. I."],["dc.contributor.author","Işık, E."],["dc.contributor.author","Sowmya, K."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Gizon, L."],["dc.date.accessioned","2022-08-01T07:35:55Z"],["dc.date.available","2022-08-01T07:35:55Z"],["dc.date.issued","2022-07-28"],["dc.date.updated","2022-07-30T02:55:06Z"],["dc.description.abstract","Surfaces of the Sun and other cool stars are filled with magnetic fields, which are either seen as dark compact spots or more diffuse bright structures like faculae. Both hamper detection and characterization of exoplanets, affecting stellar brightness and spectra, as well as transmission spectra. However, the expected facular and spot signals in stellar data are quite different, for instance, they have distinct temporal and spectral profiles. Consequently, corrections of stellar data for magnetic activity can greatly benefit from the insight on whether the stellar signal is dominated by spots or faculae. Here, we utilize a surface flux transport model to show that more effective cancellation of diffuse magnetic flux associated with faculae leads to spot area coverages increasing faster with stellar magnetic activity than that by faculae. Our calculations explain the observed dependence between solar spot and facular area coverages and allow its extension to stars that are more active than the Sun. This extension enables anticipating the properties of stellar signal and its more reliable mitigation, leading to a more accurate characterization of exoplanets and their atmospheres."],["dc.description.sponsorship","A. I. Shapiro"],["dc.identifier.doi","10.3847/2041-8213/ac8155"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/112556"],["dc.language.iso","en"],["dc.relation.eissn","2041-8213"],["dc.relation.issn","2041-8205"],["dc.rights","CC BY 4.0"],["dc.rights.uri","http://creativecommons.org/licenses/by/4.0/"],["dc.title","Faculae Cancel out on the Surfaces of Active Suns"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1"],["dc.bibliographiccitation.issue","1-2"],["dc.bibliographiccitation.journal","Solar Physics"],["dc.bibliographiccitation.lastpage","26"],["dc.bibliographiccitation.volume","271"],["dc.contributor.author","Schunker, H."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Gizon, L."],["dc.contributor.author","Moradi, H."],["dc.date.accessioned","2017-09-07T11:48:42Z"],["dc.date.available","2017-09-07T11:48:42Z"],["dc.date.issued","2011"],["dc.description.abstract","In local helioseismology, numerical simulations of wave propagation are useful to model the interaction of solar waves with perturbations to a background solar model. However, the solution to the linearised equations of motion include convective modes that can swamp the helioseismic waves that we are interested in. In this article, we construct background solar models that are stable against convection, by modifying the vertical pressure gradient of Model S (Christensen-Dalsgaard et al., 1996, Science 272, 1286) relinquishing hydrostatic equilibrium. However, the stabilisation affects the eigenmodes that we wish to remain as close to Model S as possible. In a bid to recover the Model S eigenmodes, we choose to make additional corrections to the sound speed of Model S before stabilisation. No stabilised model can be perfectly solar-like, so we present three stabilised models with slightly different eigenmodes. The models are appropriate to study the f and p 1 to p 4 modes with spherical harmonic degrees in the range from 400 to 900. Background model CSM has a modified pressure gradient for stabilisation and has eigenfrequencies within 2% of Model S. Model CSM_A has an additional 10% increase in sound speed in the top 1 Mm resulting in eigenfrequencies within 2% of Model S and eigenfunctions that are, in comparison with CSM, closest to those of Model S. Model CSM_B has a 3% decrease in sound speed in the top 5 Mm resulting in eigenfrequencies within 1% of Model S and eigenfunctions that are only marginally adversely affected. These models are useful to study the interaction of solar waves with embedded three-dimensional heterogeneities, such as convective flows and model sunspots. We have also calculated the response of the stabilised models to excitation by random near-surface sources, using simulations of the propagation of linear waves. We find that the simulated power spectra of wave motion are in good agreement with an observed SOHO/MDI power spectrum. Overall, our convectively stabilised background models provide a good basis for quantitative numerical local helioseismology. The models are available for download from http://www.mps.mpg.de/projects/seismo/NA4/ ."],["dc.identifier.doi","10.1007/s11207-011-9790-x"],["dc.identifier.gro","3147041"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/7173"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/4773"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","0038-0938"],["dc.relation.orgunit","Wirtschaftswissenschaftliche Fakultät"],["dc.rights","Goescholar"],["dc.rights.uri","https://goescholar.uni-goettingen.de/licenses"],["dc.title","Constructing and Characterising Solar Structure Models for Computational Helioseismology"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1469"],["dc.bibliographiccitation.issue","6498"],["dc.bibliographiccitation.journal","Science"],["dc.bibliographiccitation.lastpage","1472"],["dc.bibliographiccitation.volume","368"],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Cameron, Robert H."],["dc.contributor.author","Pourabdian, Majid"],["dc.contributor.author","Liang, Zhi-Chao"],["dc.contributor.author","Fournier, Damien"],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Hanson, Chris S."],["dc.date.accessioned","2021-03-05T08:59:01Z"],["dc.date.available","2021-03-05T08:59:01Z"],["dc.date.issued","2020"],["dc.identifier.doi","10.1126/science.aaz7119"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/80330"],["dc.language.iso","en"],["dc.notes.intern","DOI Import GROB-393"],["dc.relation.eissn","1095-9203"],["dc.relation.issn","0036-8075"],["dc.title","Meridional flow in the Sun’s convection zone is a single cell in each hemisphere"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","309"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Solar Physics"],["dc.bibliographiccitation.lastpage","320"],["dc.bibliographiccitation.volume","268"],["dc.contributor.author","Daiffallah, K."],["dc.contributor.author","Abdelatif, T."],["dc.contributor.author","Bendib, A."],["dc.contributor.author","Cameron, R."],["dc.contributor.author","Gizon, Laurent"],["dc.date.accessioned","2021-03-05T09:05:23Z"],["dc.date.available","2021-03-05T09:05:23Z"],["dc.date.issued","2010"],["dc.identifier.doi","10.1007/s11207-010-9666-5"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/80456"],["dc.language.iso","en"],["dc.notes.intern","DOI Import GROB-393"],["dc.relation.eissn","1573-093X"],["dc.relation.issn","0038-0938"],["dc.title","3D Numerical Simulations of f-Mode Propagation Through Magnetic Flux Tubes"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.issue","7"],["dc.bibliographiccitation.journal","Science Advances"],["dc.bibliographiccitation.volume","2"],["dc.contributor.author","Birch, Aaron C."],["dc.contributor.author","Schunker, H."],["dc.contributor.author","Braun, D. C."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Löptien, Björn"],["dc.contributor.author","Rempel, M."],["dc.date.accessioned","2017-09-07T11:49:43Z"],["dc.date.available","2017-09-07T11:49:43Z"],["dc.date.issued","2016"],["dc.description.abstract","Magnetic field emerges at the surface of the Sun as sunspots and active regions. This process generates a poloidal magnetic field from a rising toroidal flux tube; it is a crucial but poorly understood aspect of the solar dynamo. The emergence of magnetic field is also important because it is a key driver of solar activity. We show that measurements of horizontal flows at the solar surface around emerging active regions, in combination with numerical simulations of solar magnetoconvection, can constrain the subsurface rise speed of emerging magnetic flux. The observed flows imply that the rise speed of the magnetic field is no larger than 150 m/s at a depth of 20 Mm, that is, well below the prediction of the (standard) thin flux tube model but in the range expected for convective velocities at this depth. We conclude that convective flows control the dynamics of rising flux tubes in the upper layers of the Sun and cannot be neglected in models of flux emergence."],["dc.identifier.doi","10.1126/sciadv.1600557"],["dc.identifier.gro","3147404"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/4994"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","2375-2548"],["dc.title","A low upper limit on the subsurface rise speed of solar active regions"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dc.type.peerReviewed","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A16"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","662"],["dc.contributor.author","Bekki, Yuto"],["dc.contributor.author","Cameron, Robert H."],["dc.contributor.author","Gizon, Laurent"],["dc.date.accessioned","2022-07-01T07:34:57Z"],["dc.date.available","2022-07-01T07:34:57Z"],["dc.date.issued","2022"],["dc.description.abstract","Context. Several types of global-scale inertial modes of oscillation have been observed on the Sun. These include the equatorial Rossby modes, critical-latitude modes, and high-latitude modes. However, the columnar convective modes (predicted by simulations and also known as banana cells or thermal Rossby waves) remain elusive. Aims. We aim to investigate the influence of turbulent diffusivities, non-adiabatic stratification, differential rotation, and a latitudinal entropy gradient on the linear global modes of the rotating solar convection zone. Methods. We numerically solved for the eigenmodes of a rotating compressible fluid inside a spherical shell. The model takes into account the solar stratification, turbulent diffusivities, differential rotation (determined by helioseismology), and the latitudinal entropy gradient. As a starting point, we restricted ourselves to a superadiabaticity and turbulent diffusivities that are uniform in space. We identified modes in the inertial frequency range, including the columnar convective modes as well as modes of a mixed character. The corresponding mode dispersion relations and eigenfunctions are computed for azimuthal orders of m  ≤ 16. Results. The three main results are as follows. Firstly, we find that, for m  ≳ 5, the radial dependence of the equatorial Rossby modes with no radial node ( n  = 0) is radically changed from the traditional expectation ( r m ) for turbulent diffusivities ≳10 12 cm 2 s −1 . Secondly, we find mixed modes, namely, modes that share properties of the equatorial Rossby modes with one radial node ( n  = 1) and the columnar convective modes, which are not substantially affected by turbulent diffusion. Thirdly, we show that the m  = 1 high-latitude mode in the model is consistent with the solar observations when the latitudinal entropy gradient corresponding to a thermal wind balance is included (baroclinically unstable mode). Conclusions. To our knowledge, this work is the first realistic eigenvalue calculation of the global modes of the rotating solar convection zone. This calculation reveals a rich spectrum of modes in the inertial frequency range, which can be directly compared to the observations. In turn, the observed modes can inform us about the solar convection zone."],["dc.identifier.doi","10.1051/0004-6361/202243164"],["dc.identifier.pii","aa43164-22"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/112047"],["dc.notes.intern","DOI-Import GROB-581"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Theory of solar oscillations in the inertial frequency range: Linear modes of the convection zone"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A65"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","637"],["dc.contributor.author","Damiani, C."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Birch, A. C."],["dc.contributor.author","Gizon, Laurent"],["dc.date.accessioned","2021-03-05T08:58:36Z"],["dc.date.available","2021-03-05T08:58:36Z"],["dc.date.issued","2020"],["dc.identifier.doi","10.1051/0004-6361/201936251"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/80196"],["dc.notes.intern","DOI Import GROB-393"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Rossby modes in slowly rotating stars: depth dependence in distorted polytropes with uniform rotation"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A116"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","640"],["dc.contributor.author","Schunker, Hannah"],["dc.contributor.author","Baumgartner, C."],["dc.contributor.author","Birch, A. C."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Braun, D. C."],["dc.contributor.author","Gizon, Laurent"],["dc.date.accessioned","2021-03-05T08:58:37Z"],["dc.date.available","2021-03-05T08:58:37Z"],["dc.date.issued","2020"],["dc.identifier.doi","10.1051/0004-6361/201937322"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/80198"],["dc.notes.intern","DOI Import GROB-393"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Average motion of emerging solar active region polarities"],["dc.title.alternative","II. Joy’s law"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]