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R. Rezaei - One of the best experts on this subject based on the ideXlab platform.
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The magnetic nature of Umbra–penUmbra boundary in sunspots
Astronomy and Astrophysics, 2018Co-Authors: J Jurcak, Rolf Schlichenmaier, N. Bello González, R. Rezaei, Jiří VomlelAbstract:Context. Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between Umbrae and penUmbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Aim. Here, we aim at studying the magnetic nature of Umbra–penUmbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. Methods. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the Umbral boundaries. We defined these Umbra–penUmbra boundaries by an intensity threshold and performed a statistical analysis of the magnetic field properties on these boundaries. Results. We statistically prove that the Umbra–penUmbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the Umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99%, in the range of 1849–1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the Umbral size: the larger the Umbra, the stronger and more horizontal the magnetic field at its boundary. Conclusions. The Umbra and penUmbra of sunspots are separated by a boundary that has hitherto been defined by an intensity threshold. We now unveil the empirical law of the magnetic nature of the Umbra–penUmbra boundary in stable sunspots: it is an invariant vertical component of the magnetic field.
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the magnetic nature of Umbra penUmbra boundary in sunspots
Astronomy and Astrophysics, 2018Co-Authors: J Jurcak, Rolf Schlichenmaier, R. Rezaei, Bello N Gonzalez, Jiří VomlelAbstract:Context. Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between Umbrae and penUmbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Aim. Here, we aim at studying the magnetic nature of Umbra–penUmbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. Methods. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the Umbral boundaries. We defined these Umbra–penUmbra boundaries by an intensity threshold and performed a statistical analysis of the magnetic field properties on these boundaries. Results. We statistically prove that the Umbra–penUmbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the Umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99%, in the range of 1849–1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the Umbral size: the larger the Umbra, the stronger and more horizontal the magnetic field at its boundary. Conclusions. The Umbra and penUmbra of sunspots are separated by a boundary that has hitherto been defined by an intensity threshold. We now unveil the empirical law of the magnetic nature of the Umbra–penUmbra boundary in stable sunspots: it is an invariant vertical component of the magnetic field.
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the magnetic nature of Umbra penUmbra boundary in sunspots
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: J Jurcak, Rolf Schlichenmaier, R. Rezaei, Nazaret Bello Gonzalez, Jiří VomlelAbstract:Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between Umbrae and penUmbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Here, we aim at studying the magnetic nature of Umbra-penUmbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the Umbral boundaries. We defined these Umbra-penUmbra boundaries by an intensity threshold and performed a statistical analysis of the magnetic field properties on these boundaries. We statistically prove that the Umbra-penUmbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the Umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99\%, in the range of 1849-1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the Umbral size: the larger the Umbra, the stronger and more horizontal the magnetic field at its boundary. The Umbra and penUmbra of sunspots are separated by a boundary that has hitherto been defined by an intensity threshold. We now unveil the empirical law of the magnetic nature of the Umbra-penUmbra boundary in stable sunspots: it is an invariant vertical component of the magnetic field.
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a distinct magnetic property of the inner penUmbral boundary ii formation of a penUmbra at the expense of a pore
Astronomy and Astrophysics, 2017Co-Authors: J Jurcak, Rolf Schlichenmaier, R. Rezaei, Bello N GonzalezAbstract:Context. We recently presented evidence that stable Umbra-penUmbra boundaries are characterised by a distinct canonical value of the vertical component of the magnetic field, B stable ver . In order to trigger the formation of a penUmbra, large inclinations in the magnetic field are necessary. In sunspots, the penUmbra develops and establishes by colonising both Umbral areas and granulation, that is, penUmbral magneto-convection takes over in Umbral regions with B ver B stable ver , as well as in granular convective areas. Eventually, a stable Umbra-penUmbra boundary settles at B stable ver . Aims. Here, we aim to study the development of a penUmbra initiated at the boundary of a pore, where the penUmbra colonises the entire pore ultimately. Methods. We have used Hinode/SOT G -band images to study the evolution of the penUmbra. Hinode/SOT spectropolarimetric data were used to infer the magnetic field properties in the studied region. Results. The penUmbra forms at the boundary of a pore located close to the polarity inversion line of NOAA 10960. As the penUmbral bright grains protrude into the pore, the magnetic flux in the forming penUmbra increases at the expense of the pore magnetic flux. Consequently, the pore disappears completely giving rise to an orphan penUmbra. At all times, the vertical component of the magnetic field in the pore is smaller than B stable ver ≈ 1.8 kG. Conclusions. Our findings are in an agreement with the need of B stable ver for establishing a stable Umbra-penUmbra boundary: while B ver in the pore is smaller than B stable ver , the protrusion of penUmbral grains into the pore area is not blocked, a stable pore-penUmbra boundary does not establish, and the pore is fully overtaken by the penUmbral magneto-convective mode. This scenario could also be one of the mechanisms giving rise to orphan penUmbrae.
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a distinct magnetic property of the inner penUmbral boundary ii formation of a penUmbra at the expense of a pore
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: J Jurcak, Rolf Schlichenmaier, Nazaret Bello Gonzalez, R. RezaeiAbstract:We recently presented evidence that stable Umbra-penUmbra boundaries are characterised by a distinct canonical value of the vertical component of the magnetic field, $B^{\rm stable}_{\rm ver}$. In order to trigger the formation of a penUmbra, large inclinations in the magnetic field are necessary. In sunspots, the penUmbra develops and establishes by colonising both Umbral areas and granulation, that is, penUmbral magneto-convection takes over in Umbral regions with $B_{\rm ver} < B^{\rm stable}_{\rm ver}$, as well as in granular convective areas. Eventually, a stable Umbra-penUmbra boundary settles at $B^{\rm stable}_{\rm ver}$. Here, we aim to study the development of a penUmbra initiated at the boundary of a pore, where the penUmbra colonises the entire pore ultimately. We have used Hinode/SOT G-band images to study the evolution of the penUmbra. Hinode/SOT spectropolarimetric data were used to infer the magnetic field properties in the studied region. The penUmbra forms at the boundary of a pore located close to the polarity inversion line of NOAA\,10960. As the penUmbral bright grains protrude into the pore, the magnetic flux in the forming penUmbra increases at the expense of the pore magnetic flux. Consequently, the pore disappears completely giving rise to an orphan penUmbra. At all times, the vertical component of the magnetic field in the pore is smaller than $B^{\rm stable}_{\rm ver} \approx 1.8$~kG. Our findings are in an agreement with the need of $B^{\rm stable}_{\rm ver}$ for establishing a stable Umbra-penUmbra boundary: while $B_{\rm ver}$ in the pore is smaller than $B^{\rm stable}_{\rm ver}$, the protrusion of penUmbral grains into the pore area is not blocked, a stable pore-penUmbra boundary does not establish, and the pore is fully overtaken by the penUmbral magneto-convective mode. This scenario could also be one of the mechanisms giving rise to orphan penUmbrae.
J Jurcak - One of the best experts on this subject based on the ideXlab platform.
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a distinct magnetic property of the inner penUmbral boundary iii analysis of simulated sunspots
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: J Jurcak, Nazaret Bello Gonzalez, Markus Schmassmann, Matthias Rempel, Rolf SchlichenmaierAbstract:The analyses of sunspot observations revealed a fundamental magnetic property of the Umbral boundary, the invariance of the vertical component of the magnetic field. We aim to analyse the magnetic properties of the Umbra-penUmbra boundary in simulated sunspots and thus assess their similarity to observed sunspots. Also, we aim to investigate the role of plasma $\beta$ and the ratio of kinetic to magnetic energy in simulated sunspots on the convective motions. We use a set of non-grey simulation runs of sunspots with the MURaM code. These data are used to synthesise the Stokes profiles that are then degraded to the Hinode spectropolarimeter-like observations. Then, the data are treated like real Hinode observations of a sunspot and magnetic properties at the Umbral boundaries are determined. Simulations with potential field extrapolation produce a realistic magnetic field configuration on their Umbral boundaries. Two simulations with potential field upper boundary, but different subsurface magnetic field structures, differ significantly in the extent of their penUmbrae. Increasing the penUmbra width by forcing more horizontal magnetic fields at the upper boundary results in magnetic properties that are not consistent with observations. This implies that the size of the penUmbra is given by the subsurface structure of the magnetic field. None of the sunspot simulations is consistent with observed properties of the magnetic field and direction of the Evershed flow at the same time. Strong outward directed Evershed flows are only found in setups with artificially enhanced horizontal component of the magnetic field at the top boundary that are not consistent with the observed magnetic field properties at the UP boundary. We want to stress out that the `photospheric' boundary of simulated sunspots is defined by a magnetic field strength of equipartition field value.
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The magnetic nature of Umbra–penUmbra boundary in sunspots
Astronomy and Astrophysics, 2018Co-Authors: J Jurcak, Rolf Schlichenmaier, N. Bello González, R. Rezaei, Jiří VomlelAbstract:Context. Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between Umbrae and penUmbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Aim. Here, we aim at studying the magnetic nature of Umbra–penUmbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. Methods. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the Umbral boundaries. We defined these Umbra–penUmbra boundaries by an intensity threshold and performed a statistical analysis of the magnetic field properties on these boundaries. Results. We statistically prove that the Umbra–penUmbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the Umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99%, in the range of 1849–1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the Umbral size: the larger the Umbra, the stronger and more horizontal the magnetic field at its boundary. Conclusions. The Umbra and penUmbra of sunspots are separated by a boundary that has hitherto been defined by an intensity threshold. We now unveil the empirical law of the magnetic nature of the Umbra–penUmbra boundary in stable sunspots: it is an invariant vertical component of the magnetic field.
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the magnetic nature of Umbra penUmbra boundary in sunspots
Astronomy and Astrophysics, 2018Co-Authors: J Jurcak, Rolf Schlichenmaier, R. Rezaei, Bello N Gonzalez, Jiří VomlelAbstract:Context. Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between Umbrae and penUmbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Aim. Here, we aim at studying the magnetic nature of Umbra–penUmbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. Methods. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the Umbral boundaries. We defined these Umbra–penUmbra boundaries by an intensity threshold and performed a statistical analysis of the magnetic field properties on these boundaries. Results. We statistically prove that the Umbra–penUmbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the Umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99%, in the range of 1849–1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the Umbral size: the larger the Umbra, the stronger and more horizontal the magnetic field at its boundary. Conclusions. The Umbra and penUmbra of sunspots are separated by a boundary that has hitherto been defined by an intensity threshold. We now unveil the empirical law of the magnetic nature of the Umbra–penUmbra boundary in stable sunspots: it is an invariant vertical component of the magnetic field.
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the magnetic nature of Umbra penUmbra boundary in sunspots
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: J Jurcak, Rolf Schlichenmaier, R. Rezaei, Nazaret Bello Gonzalez, Jiří VomlelAbstract:Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between Umbrae and penUmbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Here, we aim at studying the magnetic nature of Umbra-penUmbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the Umbral boundaries. We defined these Umbra-penUmbra boundaries by an intensity threshold and performed a statistical analysis of the magnetic field properties on these boundaries. We statistically prove that the Umbra-penUmbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the Umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99\%, in the range of 1849-1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the Umbral size: the larger the Umbra, the stronger and more horizontal the magnetic field at its boundary. The Umbra and penUmbra of sunspots are separated by a boundary that has hitherto been defined by an intensity threshold. We now unveil the empirical law of the magnetic nature of the Umbra-penUmbra boundary in stable sunspots: it is an invariant vertical component of the magnetic field.
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a distinct magnetic property of the inner penUmbral boundary ii formation of a penUmbra at the expense of a pore
Astronomy and Astrophysics, 2017Co-Authors: J Jurcak, Rolf Schlichenmaier, R. Rezaei, Bello N GonzalezAbstract:Context. We recently presented evidence that stable Umbra-penUmbra boundaries are characterised by a distinct canonical value of the vertical component of the magnetic field, B stable ver . In order to trigger the formation of a penUmbra, large inclinations in the magnetic field are necessary. In sunspots, the penUmbra develops and establishes by colonising both Umbral areas and granulation, that is, penUmbral magneto-convection takes over in Umbral regions with B ver B stable ver , as well as in granular convective areas. Eventually, a stable Umbra-penUmbra boundary settles at B stable ver . Aims. Here, we aim to study the development of a penUmbra initiated at the boundary of a pore, where the penUmbra colonises the entire pore ultimately. Methods. We have used Hinode/SOT G -band images to study the evolution of the penUmbra. Hinode/SOT spectropolarimetric data were used to infer the magnetic field properties in the studied region. Results. The penUmbra forms at the boundary of a pore located close to the polarity inversion line of NOAA 10960. As the penUmbral bright grains protrude into the pore, the magnetic flux in the forming penUmbra increases at the expense of the pore magnetic flux. Consequently, the pore disappears completely giving rise to an orphan penUmbra. At all times, the vertical component of the magnetic field in the pore is smaller than B stable ver ≈ 1.8 kG. Conclusions. Our findings are in an agreement with the need of B stable ver for establishing a stable Umbra-penUmbra boundary: while B ver in the pore is smaller than B stable ver , the protrusion of penUmbral grains into the pore area is not blocked, a stable pore-penUmbra boundary does not establish, and the pore is fully overtaken by the penUmbral magneto-convective mode. This scenario could also be one of the mechanisms giving rise to orphan penUmbrae.
Anirvan Dasgupta - One of the best experts on this subject based on the ideXlab platform.
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Revisiting Umbra-Lagrangian–Hamiltonian mechanics: Its variational foundation and extension of Noether's theorem and Poincare–Cartan integral
International Journal of Non-linear Mechanics, 2011Co-Authors: Amalendu Mukherjee, Vikas Rastogi, Anirvan DasguptaAbstract:Abstract This paper revisits an extension of the Lagrangian–Hamiltonian mechanics that incorporates dissipative and non-potential fields, and non-integrable constraints in a compact form, such that one may obtain invariants of motion or possible invariant trajectories through an extension of Noether's theorem. A new concept of Umbra-time has been introduced for this extension. This leads to a new form of equation, which is termed as the Umbra-Lagrange's equation. The underlying variational principle, which is based on a recursive minimization of functionals, is presented. The introduction of the concept of Umbra-time extends the classical manifold over which the system evolves. An extension of the Lagrangian–Hamiltonian mechanics over vector fields in this extended space has been presented. The idea of Umbra time is then carried forward to propose the basic concept of Umbra-Hamiltonian, which is used along with the extended Noether's theorem to provide an insight into the dynamics of systems with symmetries. Gauge functions for Umbra-Lagrangian are also introduced. Extension of the Poincare–Cartan integral for the Umbra-Lagrangian theory is also proposed, and its implications have been discussed. Several examples are presented to illustrate all these concepts.
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revisiting Umbra lagrangian hamiltonian mechanics its variational foundation and extension of noether s theorem and poincare cartan integral
International Journal of Non-linear Mechanics, 2011Co-Authors: Amalendu Mukherjee, Vikas Rastogi, Anirvan DasguptaAbstract:Abstract This paper revisits an extension of the Lagrangian–Hamiltonian mechanics that incorporates dissipative and non-potential fields, and non-integrable constraints in a compact form, such that one may obtain invariants of motion or possible invariant trajectories through an extension of Noether's theorem. A new concept of Umbra-time has been introduced for this extension. This leads to a new form of equation, which is termed as the Umbra-Lagrange's equation. The underlying variational principle, which is based on a recursive minimization of functionals, is presented. The introduction of the concept of Umbra-time extends the classical manifold over which the system evolves. An extension of the Lagrangian–Hamiltonian mechanics over vector fields in this extended space has been presented. The idea of Umbra time is then carried forward to propose the basic concept of Umbra-Hamiltonian, which is used along with the extended Noether's theorem to provide an insight into the dynamics of systems with symmetries. Gauge functions for Umbra-Lagrangian are also introduced. Extension of the Poincare–Cartan integral for the Umbra-Lagrangian theory is also proposed, and its implications have been discussed. Several examples are presented to illustrate all these concepts.
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A Study of a Bi-symmetric Electro-mechanical System through Umbra-Lagrangian Generated by Bondgraphs, and Noether's Theorem
SIMULATION, 2007Co-Authors: Amalendu Mukherjee, Vikas Rastogi, Anirvan DasguptaAbstract:This paper presents a dynamic analysis of an electro-mechanical system through the Umbra-Lagrange's equation proposed in a previous paper, which includes dissipative and non-potential fields in a compact Lagrangian form. An eXtended Noether's theorem along with an Umbra-Hamiltonian is employed to get invariants of motion, or possible invariant trajectories. The Umbra-Lagrangian of this electro-mechanical system is obtained through an eXtended Karnopp's algorithm. The major contribution of this paper is the dynamic analysis eXploiting the symmetries of an electromechanical system comprising an eXternally and internally damped, symmetric, elastic rotor driven by a two-phase induction motor. For such a system the Umbra-Lagrangian remains unchanged under two families of continuous transformations. The behavior of the limiting dynamics is obtained and validated through simulations. The stability issue of this system is also eXamined. Similar analysis is also eXtended to an identical rotor driven by a three-phase induction motor. As SO (2) symmetries are not obvious in this case due to the presence of three stator inertances, the three-phase induction motor is reduced to an equivalent SO (2) symmetric two-phase induction motor, to which the analysis is applied.
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a methodology for finding invariants of motion for asymmetric systems with gauge transformed Umbra lagrangian generated by bond graphs
International Conference on Advances in System Simulation, 2006Co-Authors: Amalendu Mukherjee, Vikas Rastogi, Anirvan DasguptaAbstract:The purpose of this article is to obtain conservation laws (invariants of motion) for different energy domains through the extended Noether theorem and bond graphs. Bond graphs are profitably used in representing the physics of a system as well as obtaining its Umbra-Lagrangian. The article extends Lagrangian-Hamiltonian mechanics to deal with asymmetries in the system, which incorporates dissipative and nonpotential fields in a compact Lagrangian form, such that one may obtain invariants of motion through extension of Noether's theorem. A detailed methodology is outlined in this article for obtaining the invariants of motion for a general class of asymmetric systems with a gauge-transformed Umbra-Lagrangian. Symmetrization of an asymmetric system is introduced through the concept of gauge functions, for which the classical Noether theorem is extended over vector fields in the extended manifold comprising real and Umbra displacements and velocities, as well as real time. A generalization of the variational principle or least action principle is also presented, which leads to the proposed form of the Umbra-Lagrange equation through recursive minimization of functionals. Several illustrative examples are given to elucidate this concept in different physical contexts.
V M Nakariakov - One of the best experts on this subject based on the ideXlab platform.
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wave dynamics in a sunspot Umbra
Astronomy and Astrophysics, 2014Co-Authors: R A Sych, V M NakariakovAbstract:Context. Sunspot oscillations are one of the most frequently studied wave phenomena in the solar atmosphere. Understanding the basic physical processes responsible for sunspot oscillations requires detailed information about their fine structure. Aims. We aim to reveal the relationship between the fine horizontal and vertical structure, time evolution, and the fine spectral structure of oscillations in a sunspot Umbra. Methods. The high spatial and time resolution data obtained with SDO/AIA for the sunspot in active region NOAA 11131 on 08 December 2010 were analysed with the time-distance plot technique and the pixelised wavelet filtering method. Different levels of the sunspot atmosphere were studied from the temperature minimum to the corona. Results. Oscillations in the 3 min band dominate in the Umbra. The integrated spectrum of Umbral oscillations contains distinct narrowband peaks at 1.9 min, 2.3 min, and 2.8 min. The power significantly varies in time, forming distinct 12–20 min oscillation trains. The oscillation power distribution over the sunspot in the horizontal plane reveals that the enhancements of the oscillation amplitude, or wave fronts, have a distinct structure consisting of an evolving two-armed spiral and a stationary circular patch at the spiral origin, situated near the Umbra centre. This structure is seen from the temperature minimum at 1700 A to the 1.6 MK corona at 193 A. In time, the spiral rotates anti-clockwise. The wave front spirality is most pronounced during the maximum amplitude phases of the oscillations, and in the bandpasses where Umbral oscillations have the highest power, 304 A and 171 A. In the low-amplitude phases the spiral breaks into arc-shaped patches. The 2D cross-correlation function shows that the oscillations at higher atmospheric levels occur later than at lower layers. The phase speed is estimated to be about 100 km s-1. The fine spectral analysis shows that the central patch corresponds to the high-frequency oscillations, while the spiral arms highlight the lower-frequency oscillations in the 3 min band. Conclusions. The vertical and horizontal radial structure of the oscillations is consistent with the model that interprets Umbral oscillations as slow magnetoacoustic waves filtered by the atmospheric temperature non-uniformity in the presence of the magnetic field inclination from the vertical. The mechanism for the polar-angle structure of the oscillations, in particular the spirality of the wave fronts, needs to be revealed.
Vasyl Yurchyshyn - One of the best experts on this subject based on the ideXlab platform.
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Spatial Distribution of Origin of Umbral Waves in a Sunspot Umbra.
The Astrophysical Journal, 2020Co-Authors: Vasyl Yurchyshyn, Ali Kilcik, Seray Sahin, Valentina I. Abramenko, Eun-kyung LimAbstract:Umbral flashes (UFs) are emissions in the core of chromospheric lines caused by upward propagating waves steepening into shocks. UFs are followed by an expanding blue shifted Umbral wave (UW) and red-shifted plasma returning to the initial state. Here we use 5 s cadence images acquired at $\pm$0.04~nm off the Halpha line center by the Visible Imaging Spectrometer (VIS) installed on the Goode Solar Telescope (GST) to detect the origin of UFs and UWs in a sunspot with a uniform Umbra free of LBs and clusters of Umbral dots. The data showed that UFs do not randomly originate over the Umbra. Instead, they appear to be repeatedly triggered at locations with the lowest Umbral intensity and the most powerful oscillations of Halpha-0.04 nm intensity. GST magnetic field measurements using Near Infra-Red Imaging Spectropolarimeter (NIRIS) also showed that the dominant location of prevalent UF origin is co-spatial associated with the strongest fields in the Umbra. Interface Region Imaging Spectrograph 149.0 nm images showed that no bright UV loops were anchored in the Umbra in general and near the UF patches in particular suggesting that UFs and UWs alone can not be responsible for the origin of warm coronal loops. We thus conclude that the existence of locations with prevalent origin of UFs confirms the idea that they may be driven by a sub-surface source located near the axis of a flux rope, while the presence of several UFs trigger centers may indicate the complex structure of a sunspot Umbra.
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Dynamics in Sunspot Umbra as Seen in New Solar Telescope and Interface Region Imaging Spectrograph Data
The Astrophysical Journal, 2015Co-Authors: Vasyl Yurchyshyn, Valentyna Abramenko, Ali KilcikAbstract:We analyze sunspot oscillations using Interface Region Imaging Spectrograph (IRIS) slit-jaw and spectral data and narrow-band chromospheric images from the New Solar Telescope (NST) for the main sunspot in NOAA AR 11836. We report that the difference between the shock arrival times as measured by the Mg II k 2796.35 ? and Si IV 1393.76 ? line formation levels changes during the observed period, and peak-to-peak delays may range from 40 s to zero. The intensity of chromospheric shocks also displays long-term (about 20?min) variations. NST's high spatial resolution H? data allowed us to conclude that, in this sunspot, Umbral flashes (UFs) appeared in the form of narrow bright lanes stretched along the light bridges and around clusters of Umbral bright points. The time series also suggested that UFs preferred to appear on the sunspot-center side of light bridges, which may indicate the existence of a compact sub-photospheric driver of sunspot oscillations. The sunspot's Umbra as seen in the IRIS chromospheric and transition region data appears bright above the locations of light bridges and the areas where the dark Umbra is dotted with clusters of Umbral dots. Co-spatial and co-temporal data from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory showed that the same locations were associated with bright footpoints of coronal loops suggesting that the light bridges may play an important role in heating the coronal sunspot loops. Finally, the power spectra analysis showed that the intensity of chromospheric and transition region oscillations significantly vary across the Umbra and with height, suggesting that Umbral non-uniformities and the structure of sunspot magnetic fields may play a role in wave propagation and heating of Umbral loops.
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dynamics in sunspot Umbra as seen in new solar telescope and interface region imaging spectrograph data
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: Vasyl Yurchyshyn, Valentyna Abramenko, A KilcikAbstract:We analyse sunspot oscillations using Interface Region Imaging Spectrograph (IRIS) slit-jaw and spectral data and narrow-band chromospheric images from the New Solar Telescope (NST) for the main sunspot in NOAA AR 11836. We report that the difference between the shock arrival times as measured the Mg II k 2796.35\AA\ and Si IV 1393.76\AA\ line formation levels changes during the observed period and peak-to-peak delays may range from 40~s to zero. The intensity of chromospheric shocks also displays a long term (about 20~min) variations. NST's high spatial resolution \ha\ data allowed us to conclude that in this sunspot Umbral flashes (UFs) appeared in the form of narrow bright lanes stretched along the light bridges and around clusters of Umbral bright points. Time series also suggested that UFs preferred to appear on the sunspot-center side of light bridges, which may indicate the existence of a compact sub-photospheric driver of sunspot oscillations. The sunspot's Umbra as seen in the IRIS chromospheric and transition region data appears bright above the locations of light bridges and the areas where the dark Umbra is dotted with clusters of Umbral dots. Co-spatial and co-temporal data from the Atmospheric Imaging Assembly on board Solar Dynamics Observatory showed that the same locations were associated with bright footpoints of coronal loops suggesting that the light bridges may play an important role in heating the coronal sunspot loops. Finally, the power spectra analysis showed that the intensity of chromospheric and transition region oscillations significantly vary across the Umbra and with height, suggesting that Umbral non-uniformities and the structure of sunspot magnetic fields may play a role in wave propagation and heating of Umbral loops.
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High Resolution Observations of Chromospheric Jets in Sunspot Umbra
The Astrophysical Journal, 2014Co-Authors: Vasyl Yurchyshyn, V. Abramenko, S. Kosovichev, Philip R. GoodeAbstract:Recent observations of sunspot's Umbra suggested that it may be finely structured at a sub-arcsecond scale representing a mix of hot and cool plasma elements. In this study we report the first detailed observations of the Umbral spikes, which are cool jet-like structures seen in the chromosphere of an Umbra. The spikes are cone-shaped features with a typical height of 0.5-1.0 Mm and a width of about 0.1 Mm. Their life time ranges from 2 to 3 min and they tend to re-appear at the same location. The spikes are not associated with photospheric Umbral dots and they rather tend to occur above darkest parts of the Umbra, where magnetic fields are strongest. The spikes exhibit up and down oscillatory motions and their spectral evolution suggests that they might be driven by upward propagating shocks generated by photospheric oscillations. It is worth noting that triggering of the running penUmbral waves seems to occur during the interval when the spikes reach their maximum height.
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high resolution observations of chromospheric jets in sunspot Umbra
The Astrophysical Journal, 2014Co-Authors: Vasyl Yurchyshyn, A G Kosovichev, V. Abramenko, Philip R. GoodeAbstract:Recent observations of a sunspot's Umbra have suggested that it may be finely structured on a subarcsecond scale representing a mix of hot and cool plasma elements. In this study, we report the first detailed observations of Umbral spikes, which are cool jet-like structures seen in the chromosphere of an Umbra. The spikes are cone-shaped features with a typical height of 0.5-1.0 Mm and a width of about 0.1 Mm. Their lifetime ranges from 2 to 3 minutes and they tend to re-appear at the same location. The spikes are not associated with photospheric Umbral dots and they instead tend to occur above the darkest parts of the Umbra where magnetic fields are strongest. The spikes exhibit up and down oscillatory motions and their spectral evolution suggests that they might be driven by upward propagating shocks generated by photospheric oscillations. It is worth noting that triggering of the running penUmbral waves seems to occur during the interval when the spikes reach their maximum height.
