Bingert, Sven

[["dc.bibliographiccitation.artnumber","A104"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","556"],["dc.contributor.author","Peter, H."],["dc.contributor.author","Bingert, Sven"],["dc.contributor.author","Klimchuk, J. A."],["dc.contributor.author","DeForest, C."],["dc.contributor.author","Cirtain, J. W."],["dc.contributor.author","Golub, L."],["dc.contributor.author","Winebarger, A. R."],["dc.contributor.author","Kobayashi, K."],["dc.contributor.author","Korreck, K. E."],["dc.date.accessioned","2019-12-13T08:26:20Z"],["dc.date.available","2019-12-13T08:26:20Z"],["dc.date.issued","2013"],["dc.description.abstract","We will use new data from the High-resolution Coronal Imager (Hi-C) with unprecedented spatial resolution of the solar corona to investigate the structure of coronal loops down to 0.2 arcsec. During a rocket flight Hi-C provided images of the solar corona in a wavelength band around 193 A that is dominated by emission from Fe XII showing plasma at temperatures around 1.5 MK. We analyze part of the Hi-C field-of-view to study the smallest coronal loops observed so far and search for the a possible sub-structuring of larger loops. We find tiny 1.5 MK loop-like structures that we interpret as miniature coronal loops. These have length of the coronal segment above the chromosphere of only about 1 Mm and a thickness of less than 200 km. They could be interpreted as the coronal signature of small flux tubes breaking through the photosphere with a footpoint distance corresponding to the diameter of a cell of granulation. We find loops that are longer than 50 Mm to have a diameter of about 2 arcsec or 1.5 Mm, consistent with previous observations. However, Hi-C really resolves these loops with some 20 pixels across the loop. Even at this greatly improved spatial resolution the large loops seem to have no visible sub-structure. Instead they show a smooth variation in cross-section. The fact that the large coronal loops do not show a sub-structure at the spatial scale of 0.1 arcsec per pixel implies that either the densities and temperatures are smoothly varying across these loops or poses an upper limit on the diameter of strands the loops might be composed of. We estimate that strands that compose the 2 arcsec thick loop would have to be thinner than 15 km. The miniature loops we find for the first time pose a challenge to be properly understood in terms of modeling."],["dc.identifier.arxiv","1306.4685v1"],["dc.identifier.doi","10.1051/0004-6361/201321826"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/62748"],["dc.language.iso","en"],["dc.relation.issn","0004-6361"],["dc.relation.issn","1432-0746"],["dc.title","Structure of solar coronal loops: from miniature to large-scale"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","548"],["dc.contributor.author","Peter, H."],["dc.contributor.author","Bingert, Sven"],["dc.date.accessioned","2019-12-13T08:31:09Z"],["dc.date.available","2019-12-13T08:31:09Z"],["dc.date.issued","2012"],["dc.description.abstract","The corona of the Sun is dominated by emission from loop-like structures. When observed in X-ray or extreme ultraviolet emission, these million K hot coronal loops show a more or less constant cross section. In this study we show how the interplay of heating, radiative cooling, and heat conduction in an expanding magnetic structure can explain the observed constant cross section. We employ a three-dimensional magnetohydrodynamics (3D MHD) model of the corona. The heating of the coronal plasma is the result of braiding of the magnetic field lines through footpoint motions and subsequent dissipation of the induced currents. From the model we synthesize the coronal emission, which is directly comparable to observations from, e.g., the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (AIA/SDO). We find that the synthesized observation of a coronal loop seen in the 3D data cube does match actually observed loops in count rate and that the cross section is roughly constant, as observed. The magnetic field in the loop is expanding and the plasma density is concentrated in this expanding loop; however, the temperature is not constant perpendicular to the plasma loop. The higher temperature in the upper outer parts of the loop is so high that this part of the loop is outside the contribution function of the respective emission line(s). In effect, the upper part of the plasma loop is not bright and thus the loop actually seen in coronal emission appears to have a constant width. From this we can conclude that the underlying field-line-braiding heating mechanism provides the proper spatial and temporal distribution of the energy input into the corona --- at least on the observable scales."],["dc.identifier.arxiv","1209.0789v1"],["dc.identifier.doi","10.1051/0004-6361/201219473"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/62750"],["dc.language.iso","en"],["dc.relation.issn","0004-6361"],["dc.relation.issn","1432-0746"],["dc.title","Constant cross section of loops in the solar corona"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A12"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","564"],["dc.contributor.author","Chen, F."],["dc.contributor.author","Peter, H."],["dc.contributor.author","Bingert, S."],["dc.contributor.author","Cheung, M. C. M."],["dc.date.accessioned","2018-03-05T14:43:06Z"],["dc.date.available","2018-03-05T14:43:06Z"],["dc.date.issued","2014"],["dc.description.abstract","Aims. We present the first model that couples the formation of the corona of a solar active region to a model of the emergence of a sunspot pair. This allows us to study when, where, and why active region loops form, and how they evolve. Methods. We use a 3D radiation magnetohydrodynamics (MHD) simulation of the emergence of an active region through the upper convection zone and the photosphere as a lower boundary for a 3D MHD coronal model. The coronal model accounts for the braiding of the magnetic fieldlines, which induces currents in the corona to heat up the plasma. We synthesize the coronal emission for a direct comparison to observations. Starting with a basically field-free atmosphere we follow the filling of the corona with magnetic field and plasma. Results. Numerous individually identifiable hot coronal loops form, and reach temperatures well above 1 MK with densities comparable to observations. The footpoints of these loops are found where small patches of magnetic flux concentrations move into the sunspots. The loop formation is triggered by an increase in upward-directed Poynting flux at their footpoints in the photosphere. In the synthesized extreme ultraviolet (EUV) emission these loops develop within a few minutes. The first EUV loop appears as a thin tube, then rises and expands significantly in the horizontal direction. Later, the spatially inhomogeneous heat input leads to a fragmented system of multiple loops or strands in a growing envelope."],["dc.identifier.arxiv","1402.5343v1"],["dc.identifier.doi","10.1051/0004-6361/201322859"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/12794"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.title","A model for the formation of the active region corona driven by magnetic flux emergence"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","492"],["dc.bibliographiccitation.issue","6"],["dc.bibliographiccitation.journal","Nature Physics"],["dc.bibliographiccitation.lastpage","495"],["dc.bibliographiccitation.volume","11"],["dc.contributor.author","Chen, F."],["dc.contributor.author","Peter, H."],["dc.contributor.author","Bingert, Sven"],["dc.contributor.author","Cheung, M. C. M."],["dc.date.accessioned","2019-12-13T08:17:20Z"],["dc.date.available","2019-12-13T08:17:20Z"],["dc.date.issued","2015"],["dc.description.abstract","The outer solar atmosphere, the corona, contains plasma at temperatures of more than a million K, more than 100 times hotter that solar surface. How this gas is heated is a fundamental question tightly interwoven with the structure of the magnetic field in the upper atmosphere. Conducting numerical experiments based on magnetohydrodynamics we account for both the evolving three-dimensional structure of the atmosphere and the complex interaction of magnetic field and plasma. Together this defines the formation and evolution of coronal loops, the basic building block prominently seen in X-rays and extreme ultraviolet (EUV) images. The structures seen as coronal loops in the EUV can evolve quite differently from the magnetic field. While the magnetic field continuously expands as new magnetic flux emerges through the solar surface, the plasma gets heated on successively emerging fieldlines creating an EUV loop that remains roughly at the same place. For each snapshot the EUV images outline the magnetic field, but in contrast to the traditional view, the temporal evolution of the magnetic field and the EUV loops can be different. Through this we show that the thermal and the magnetic evolution in the outer atmosphere of a cool star has to be treated together, and cannot be simply separated as done mostly so far."],["dc.identifier.arxiv","1505.01174v1"],["dc.identifier.doi","10.1038/nphys3315"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/62746"],["dc.language.iso","en"],["dc.relation.issn","1745-2473"],["dc.relation.issn","1745-2481"],["dc.relation.orgunit","Gesellschaft für wissenschaftliche Datenverarbeitung"],["dc.title","Magnetic Jam in the Corona of the Sun"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A152"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","537"],["dc.contributor.author","Peter, H."],["dc.contributor.author","Bingert, Sven"],["dc.contributor.author","Kamio, S."],["dc.date.accessioned","2019-12-13T08:42:08Z"],["dc.date.available","2019-12-13T08:42:08Z"],["dc.date.issued","2011"],["dc.description.abstract","Condensations in the more than 10^6 K hot corona of the Sun are commonly observed in the extreme ultraviolet (EUV). While their contribution to the total solar EUV radiation is still a matter of debate, these condensations certainly provide a valuable tool for studying the dynamic response of the corona to the heating processes. We investigate different distributions of energy input in time and space to investigate which process is most relevant for understanding these coronal condensations. For a comparison to observations we synthesize EUV emission from a time-dependent, one-dimensional model for coronal loops, where we employ two heating scenarios: simply shutting down the heating and a model where the heating is very concentrated at the loop footpoints, while keeping the total heat input constant. The heating off/on model does not lead to significant EUV count rates that one observes with SDO/AIA. In contrast, the concentration of the heating near the footpoints leads to thermal non-equilibrium near the loop top resulting in the well-known catastrophic cooling. This process gives a good match to observations of coronal condensations. This shows that the corona needs a steady supply of energy to support the coronal plasma, even during coronal condensations. Otherwise the corona would drain very fast, too fast to even form a condensation."],["dc.identifier.arxiv","1112.3667v1"],["dc.identifier.doi","10.1051/0004-6361/201117889"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/62755"],["dc.language.iso","en"],["dc.relation.issn","0004-6361"],["dc.relation.issn","1432-0746"],["dc.title","Catastrophic cooling and cessation of heating in the solar corona"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A112"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","532"],["dc.contributor.author","Zacharias, P."],["dc.contributor.author","Peter, H."],["dc.contributor.author","Bingert, Sven"],["dc.date.accessioned","2019-12-13T08:40:22Z"],["dc.date.available","2019-12-13T08:40:22Z"],["dc.date.issued","2011"],["dc.description.abstract","We investigate the processes that lead to the formation, ejection and fall of a confined plasma ejection that was observed in a numerical experiment of the solar corona. By quantifying physical parameters such as mass, velocity, and orientation of the plasma ejection relative to the magnetic field, we provide a description of the nature of this particular phenomenon. The time-dependent three-dimensional magnetohydrodynamic (3D MHD) equations are solved in a box extending from the chromosphere to the lower corona. The plasma is heated by currents that are induced through field line braiding as a consequence of photospheric motions. Spectra of optically thin emission lines in the extreme ultraviolet range are synthesized, and magnetic field lines are traced over time. Following strong heating just above the chromosphere, the pressure rapidly increases, leading to a hydrodynamic explosion above the upper chromosphere in the low transition region. The explosion drives the plasma, which needs to follow the magnetic field lines. The ejection is then moving more or less ballistically along the loop-like field lines and eventually drops down onto the surface of the Sun. The speed of the ejection is in the range of the sound speed, well below the Alfven velocity. The plasma ejection is basically a hydrodynamic phenomenon, whereas the rise of the heating rate is of magnetic nature. The granular motions in the photosphere lead (by chance) to a strong braiding of the magnetic field lines at the location of the explosion that in turn is causing strong currents which are dissipated. Future studies need to determine if this process is a ubiquitous phenomenon on the Sun on small scales. Data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (AIA/SDO) might provide the relevant information."],["dc.identifier.arxiv","1106.5972v1"],["dc.identifier.doi","10.1051/0004-6361/201116708"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/62754"],["dc.language.iso","en"],["dc.relation.issn","0004-6361"],["dc.relation.issn","1432-0746"],["dc.title","Ejection of cool plasma into the hot corona"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1451"],["dc.bibliographiccitation.issue","9"],["dc.bibliographiccitation.journal","Advances in Space Research"],["dc.bibliographiccitation.lastpage","1456"],["dc.bibliographiccitation.volume","43"],["dc.contributor.author","Zacharias, Pia"],["dc.contributor.author","Bingert, Sven"],["dc.contributor.author","Peter, Hardi"],["dc.contributor.author","Peter, H."],["dc.date.accessioned","2018-03-23T10:21:50Z"],["dc.date.available","2018-03-23T10:21:50Z"],["dc.date.issued","2009"],["dc.description.abstract","We study extreme-ultraviolet emission line spectra derived from three-dimensional magnetohydrodynamic models of structures in the corona. In order to investigate the effects of increased magnetic activity at photospheric levels in a numerical experiment, a much higher magnetic flux density is applied at photospheric levels as compared to the Sun. Thus, we can expect our results to highlight the differences between the Sun and more active, but still solar-like stars. We discuss signatures seen in extreme-ultraviolet emission lines synthesized from these models and compare them to signatures found in the spatial distribution and temporal evolution of Doppler shifts in lines formed in the transition region and corona. This is of major interest to test the quality of the underlying magnetohydrodynamic model to heat the corona, i.e. currents in the corona driven by photospheric motions (flux braiding)."],["dc.identifier.arxiv","0904.2312v1"],["dc.identifier.doi","10.1016/j.asr.2009.01.033"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/13133"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.title","Spectral analysis of 3D MHD models of coronal structures"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A72"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","580"],["dc.contributor.author","Bourdin, Ph.-A."],["dc.contributor.author","Bingert, S."],["dc.contributor.author","Peter, H."],["dc.date.accessioned","2018-03-05T10:14:00Z"],["dc.date.available","2018-03-05T10:14:00Z"],["dc.date.issued","2015"],["dc.description.abstract","Context. We have conducted a 3D MHD simulation of the solar corona above an active region (AR) in full scale and high resolution, which shows coronal loops, and plasma flows within them, similar to observations. Aims. We want to find the connection between the photospheric energy input by field-line braiding with the coronal energy conversion by Ohmic dissipation of induced currents. Methods. To this end we compare the coronal energy input and dissipation within our simulation domain above different fields of view, e.g. for a small loops system in the AR core. We also choose an ensemble of field lines to compare, e.g., the magnetic energy input to the heating per particle along these field lines. Results. We find an enhanced Ohmic dissipation of currents in the corona above areas that also have enhanced upwards-directed Poynting flux. These regions coincide with the regions where hot coronal loops within the AR core are observed. The coronal density plays a role in estimating the coronal temperature due to the generated heat input. A minimum flux density of about 200 Gauss is needed in the photosphere to heat a field line to coronal temperatures of about 1 MK. Conclusions. This suggests that the field-line braiding mechanism provides the coronal energy input and that the Ohmic dissipation of induced currents dominates the coronal heating mechanism."],["dc.identifier.arxiv","1507.03573v2"],["dc.identifier.doi","10.1051/0004-6361/201525839"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/12750"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.title","Coronal energy input and dissipation in a solar active region 3D MHD model"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dspace.entity.type","Publication"]]