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T Van Doorsselaere - One of the best experts on this subject based on the ideXlab platform.
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heating by Transverse Waves in simulated coronal loops
Astronomy and Astrophysics, 2017Co-Authors: K Karampelas, T Van Doorsselaere, Patrick AntoliAbstract:Context. Recent numerical studies of oscillating flux tubes have established the significance of resonant absorption in the damping of propagating Transverse oscillations in coronal loops. The nonlinear nature of the mechanism has been examined alongside the Kelvin-Helmholtz instability, which is expected to manifest in the resonant layers at the edges of the flux tubes. While these two processes have been hypothesized to heat coronal loops through the dissipation of wave energy into smaller scales, the occurring mixing with the hotter surroundings can potentially hide this effect. Aims. We aim to study the effects of wave heating from driven and standing kink Waves in a coronal loop. Methods. Using the MPI-AMRVAC code, we perform ideal, three dimensional magnetohydrodynamic (MHD) simulations of both (a) footpoint driven and (b) free standing oscillations in a straight coronal flux tube, in the presence of numerical resistivity. Results. We have observed the development of Kelvin-Helmholtz eddies at the loop boundary layer of all three models considered here, as well as an increase of the volume averaged temperature inside the loop. The main heating mechanism in our setups was Ohmic dissipation, as indicated by the higher values for the temperatures and current densities located near the footpoints. The introduction of a temperature gradient between the inner tube and the surrounding plasma, suggests that the mixing of the two regions, in the case of hotter environment, greatly increases the temperature of the tube at the site of the strongest turbulence, beyond the contribution of the aforementioned wave heating mechanism.
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modeling observed decay less oscillations as resonantly enhanced kelvin helmholtz vortices from Transverse mhd Waves and their seismological application
The Astrophysical Journal, 2016Co-Authors: Patrick Antoli, T Van Doorsselaere, I De Moortel, T YokoyamaAbstract:In the highly structured solar corona, resonant absorption is an unavoidable mechanism of energy transfer from global Transverse MHD Waves to local azimuthal Alfven Waves. Due to its localized nature, direct detection of this mechanism is extremely difficult. Yet, it is the leading theory explaining the observed fast damping of the global Transverse Waves. However, at odds with this theoretical prediction are recent observations that indicate that in the low-amplitude regime such Transverse MHD Waves can also appear decay-less, a still unsolved phenomenon. Recent numerical work has shown that Kelvin–Helmholtz instabilities (KHI) often accompany Transverse MHD Waves. In this work, we combine 3D MHD simulations and forward modeling to show that for currently achieved spatial resolution and observed small amplitudes, an apparent decay-less oscillation is obtained. This effect results from the combination of periodic brightenings produced by the KHI and the coherent motion of the KHI vortices amplified by resonant absorption. Such an effect is especially clear in emission lines forming at temperatures that capture the boundary dynamics rather than the core, and reflects the low damping character of the local azimuthal Alfven Waves resonantly coupled to the kink mode. Due to phase mixing, the detected period can vary depending on the emission line, with those sensitive to the boundary having shorter periods than those sensitive to the loop core. This allows us to estimate the density contrast at the boundary.
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the instability and non existence of multi stranded loops when driven by Transverse Waves
The Astrophysical Journal, 2016Co-Authors: N Magya, T Van DoorsselaereAbstract:In recent years, omni-present Transverse Waves have been observed in all layers of the solar atmosphere. Coronal loops are often modeled as a collection of individual strands, in order to explain their thermal behaviour and appearance. We perform 3D ideal MHD simulations to study the effect of a continuous small amplitude Transverse footpoint driving on the internal structure of a coronal loop composed of strands. The output is also converted to synthetic images, corresponding to the AIA 171 A and 193 A passbands, using FoMo. We show that the multi-stranded loop ceases to exist in the traditional sense of the word, because the plasma is efficiently mixed perpendicularly to the magnetic field, with the Kelvin-Helmholtz instability acting as the main mechanism. The final product of our simulation is mixed loop with density structures on a large range of scales, resembling a power-law. Thus, multi-stranded loops are unstable to driving by Transverse Waves, and this raises a strong doubt on the usability and applicability of coronal loop models consisting of independent strands.
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energy propagation by Transverse Waves in multiple flux tube systems using filling factors
The Astrophysical Journal, 2014Co-Authors: T Van Doorsselaere, S E Gijse, Jesse Andries, G VerthAbstract:In the last few years, it has been found that Transverse Waves are present at all times in coronal loops or spicules. Their energy has been estimated with an expression derived for bulk AlfvWaves in homogeneous media, with correspondingly uniform wave energy density and flux. The kink mode, however, is localized in space with the energy density and flux dependent on the position in the cross-sectional plane. The more relevant quantities for the kink mode are the integrals of the energy density and flux over the cross-sectional plane. The present paper provides an approximation to the energy propagated by kink modes in an ensemble of flux tubes by means of combining the analysis of single flux tube kink oscillations with a filling factor for the tube cross-sectional area. This finally allows one to compare the expressions for energy flux of Alfv´ en Waves with an ensemble of kink Waves. We find that the correction factor for the energy in kink Waves, compared to the bulk Alfv´ en Waves, is between f and 2f, where f is the density filling factor of the ensemble of flux tubes.
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statistical seismology of Transverse Waves in the solar corona
Astronomy and Astrophysics, 2013Co-Authors: T Van Doorsselaere, E Verwichte, R S White, Patrick AntoliAbstract:Context. Observations show that Transverse oscillations occur commonly in solar coronal loops. The rapid damping of these Waves has been attributed to resonant absorption. The oscillation characteristics carries information of the structuring of the corona. However, self-consistent seismological methods to extract information from individual oscillations is limited because there are less observables than model unknown parameters and the problem is underdetermined. Furthermore, it has been shown that one-to-one comparisons of the observed scaling of period and damping times with wave damping theories is misleading. Aims. We aim to investigate if seismological information can be gained from the observed scaling laws in a statistical sense. Methods. A statistical approach is used whereby scaling-laws are produced by forward modelling using distributions of values for key loop cross-sectional structuring parameters. We study two types of observations: 1) Transverse loops oscillations as seen mainly with TRACE and SDO and 2) running Transverse Waves seen with CoMP. Results. We demonstrate that the observed period-damping time scaling law does provide information about the physical damping mechanism, if observations are collected from as wide as possible range of periods and a comparison with theory is performed in a statistical sense. The distribution of the ratio of damping time over period, i.e. the quality factor, has been derived analytically and fitted to the observations. A minimum value for the quality factor of 0.65 has been found. From this, a constraint linking the ranges of possible values for the density contrast and inhomogeneity layer thickness is obtained for Transverse loop oscillations. If the layer thickness is not constrained, then the density contrast is maximally equal to 3. For Transverse Waves seen by CoMP, it is found that the ratio of maximum to minimum values for these two parameters has to be less than 2.06. i.e. the sampled values for the layer thickness and Alfven travel time comes from a relatively narrow distribution. ´ Conclusions. Now that more and more Transverse loop oscillations have been analysed, a statistical approach to coronal seismology becomes possible. Using the observed data cloud restrictions in the loop parameter space of density contrast and inhomogeneity layer thickness are found and surprisingly for the running Waves narrow distributions for loop parameters have been found.
R Olive - One of the best experts on this subject based on the ideXlab platform.
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the behavior of Transverse Waves in nonuniform solar flux tubes ii implications for coronal loop seismology
The Astrophysical Journal, 2014Co-Authors: R Sole, Marcel Goossens, Jaume Terradas, R OliveAbstract:The seismology of coronal loops using observations of damped Transverse oscillations in combination with results from theoretical models is a tool to indirectly infer physical parameters in the solar atmospheric plasma. Existing seismology schemes based on approximations of the period and damping time of kink oscillations are often used beyond their theoretical range of applicability. These approximations assume that the variation of density across the loop is confined to a nonuniform layer much thinner than the radius of the loop, but the results of the inversion problem often do not satisfy this preliminary hypothesis. Here, we determine the accuracy of the analytic approximations of the period and damping time, and the impact on seismology estimates when largely nonuniform loops are considered. We find that the accuracy of the approximations when used beyond their range of applicability is strongly affected by the form of the density profile across the loop, that is observationally unknown and so must be arbitrarily imposed as part of the theoretical model. The error associated with the analytic approximations can be larger than 50% even for relatively thin nonuniform layers. This error directly affects the accuracy of approximate seismology estimates compared to actual numerical inversions. In addition, assuming different density profiles can produce noncoincident intervals of the seismic variables in inversions of the same event. The ignorance about the true shape of density variation across the loop is an important source of error that may dispute the reliability of parameters seismically inferred assuming an ad hoc density profile.
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the behavior of Transverse Waves in nonuniform solar flux tubes i comparison of ideal and resistive results
The Astrophysical Journal, 2013Co-Authors: R Sole, Marcel Goossens, Jaume Terradas, R OliveAbstract:Magnetohydrodynamic (MHD) Waves are ubiquitously observed in the solar atmosphere. Kink Waves are a type of Transverse MHD Waves in magnetic flux tubes that are damped due to resonant absorption. The theoretical study of kink MHD Waves in solar flux tubes is usually based on the simplification that the Transverse variation of density is confined to a nonuniform layer much thinner than the radius of the tube, i.e., the so-called thin boundary approximation. Here, we develop a general analytic method to compute the dispersion relation and the eigenfunctions of ideal MHD Waves in pressureless flux tubes with Transversely nonuniform layers of arbitrary thickness. Results for kink Waves are produced and compared with fully numerical resistive MHD eigenvalue computations in the limit of small resistivity. We find that the frequency and resonant damping rate are the same in both ideal and resistive cases. The actual results for thick nonuniform layers deviate from the behavior predicted in the thin boundary approximation and strongly depend on the shape of the nonuniform layer. The eigenfunctions in ideal MHD are very different from those in resistive MHD. The ideal eigenfunctions display a global character regardless of the thickness of the nonuniform layer, while the resistive eigenfunctions are localized around the resonance and are indistinguishable from those of ordinary resistive Alfven modes. Consequently, the spatial distribution of wave energy in the ideal and resistive cases is dramatically different. This poses a fundamental theoretical problem with clear observational consequences.
Patrick Antoli - One of the best experts on this subject based on the ideXlab platform.
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energetics of the kelvin helmholtz instability induced by Transverse Waves in twisted coronal loops
Astronomy and Astrophysics, 2017Co-Authors: T A Howso, I De Moortel, Patrick AntoliAbstract:Aims. We quantify the effects of twisted magnetic fields on the development of the magnetic Kelvin-Helmholtz instability (KHI) in Transversely oscillating coronal loops. Methods. We modelled a fundamental standing kink mode in a straight, density-enhanced magnetic flux tube using the magnetohydrodynamics code, Lare3d. In order to evaluate the impact of an azimuthal component of the magnetic field, various degrees of twist were included within the flux tube’s magnetic field. Results. The process of resonant absorption is only weakly affected by the presence of a twisted magnetic field. However, the subsequent evolution of the KHI is sensitive to the strength of the azimuthal component of the field. Increased twist values inhibit the deformation of the loop’s density profile, which is associated with the growth of the instability. Despite this, much smaller scales in the magnetic field are generated when there is a non-zero azimuthal component present. Hence, the instability is more energetic in cases with (even weakly) twisted fields. Field aligned flows at the loop apex are established in a twisted regime once the instability has formed. Further, in the straight field case, there is no net vertical component of vorticity when integrated across the loop. However, the inclusion of azimuthal magnetic field generates a preferred direction for the vorticity which oscillates during the kink mode. Conclusions. The KHI may have implications for wave heating in the solar atmosphere due to the creation of small length scales and the generation of a turbulent regime. Whilst magnetic twist does suppress the development of the vortices associated with the instability, the formation of the KHI in a twisted regime will be accompanied by greater Ohmic dissipation due to the larger currents that are produced, even if only weak twist is present. The presence of magnetic twist will likely make the instability more difficult to detect in the corona, but will enhance its contribution to heating the solar atmosphere. Further, the development of velocities along the loop may have observational applications for inferring the presence of magnetic twist within coronal structures.
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heating by Transverse Waves in simulated coronal loops
Astronomy and Astrophysics, 2017Co-Authors: K Karampelas, T Van Doorsselaere, Patrick AntoliAbstract:Context. Recent numerical studies of oscillating flux tubes have established the significance of resonant absorption in the damping of propagating Transverse oscillations in coronal loops. The nonlinear nature of the mechanism has been examined alongside the Kelvin-Helmholtz instability, which is expected to manifest in the resonant layers at the edges of the flux tubes. While these two processes have been hypothesized to heat coronal loops through the dissipation of wave energy into smaller scales, the occurring mixing with the hotter surroundings can potentially hide this effect. Aims. We aim to study the effects of wave heating from driven and standing kink Waves in a coronal loop. Methods. Using the MPI-AMRVAC code, we perform ideal, three dimensional magnetohydrodynamic (MHD) simulations of both (a) footpoint driven and (b) free standing oscillations in a straight coronal flux tube, in the presence of numerical resistivity. Results. We have observed the development of Kelvin-Helmholtz eddies at the loop boundary layer of all three models considered here, as well as an increase of the volume averaged temperature inside the loop. The main heating mechanism in our setups was Ohmic dissipation, as indicated by the higher values for the temperatures and current densities located near the footpoints. The introduction of a temperature gradient between the inner tube and the surrounding plasma, suggests that the mixing of the two regions, in the case of hotter environment, greatly increases the temperature of the tube at the site of the strongest turbulence, beyond the contribution of the aforementioned wave heating mechanism.
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modeling observed decay less oscillations as resonantly enhanced kelvin helmholtz vortices from Transverse mhd Waves and their seismological application
The Astrophysical Journal, 2016Co-Authors: Patrick Antoli, T Van Doorsselaere, I De Moortel, T YokoyamaAbstract:In the highly structured solar corona, resonant absorption is an unavoidable mechanism of energy transfer from global Transverse MHD Waves to local azimuthal Alfven Waves. Due to its localized nature, direct detection of this mechanism is extremely difficult. Yet, it is the leading theory explaining the observed fast damping of the global Transverse Waves. However, at odds with this theoretical prediction are recent observations that indicate that in the low-amplitude regime such Transverse MHD Waves can also appear decay-less, a still unsolved phenomenon. Recent numerical work has shown that Kelvin–Helmholtz instabilities (KHI) often accompany Transverse MHD Waves. In this work, we combine 3D MHD simulations and forward modeling to show that for currently achieved spatial resolution and observed small amplitudes, an apparent decay-less oscillation is obtained. This effect results from the combination of periodic brightenings produced by the KHI and the coherent motion of the KHI vortices amplified by resonant absorption. Such an effect is especially clear in emission lines forming at temperatures that capture the boundary dynamics rather than the core, and reflects the low damping character of the local azimuthal Alfven Waves resonantly coupled to the kink mode. Due to phase mixing, the detected period can vary depending on the emission line, with those sensitive to the boundary having shorter periods than those sensitive to the loop core. This allows us to estimate the density contrast at the boundary.
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statistical seismology of Transverse Waves in the solar corona
Astronomy and Astrophysics, 2013Co-Authors: T Van Doorsselaere, E Verwichte, R S White, Patrick AntoliAbstract:Context. Observations show that Transverse oscillations occur commonly in solar coronal loops. The rapid damping of these Waves has been attributed to resonant absorption. The oscillation characteristics carries information of the structuring of the corona. However, self-consistent seismological methods to extract information from individual oscillations is limited because there are less observables than model unknown parameters and the problem is underdetermined. Furthermore, it has been shown that one-to-one comparisons of the observed scaling of period and damping times with wave damping theories is misleading. Aims. We aim to investigate if seismological information can be gained from the observed scaling laws in a statistical sense. Methods. A statistical approach is used whereby scaling-laws are produced by forward modelling using distributions of values for key loop cross-sectional structuring parameters. We study two types of observations: 1) Transverse loops oscillations as seen mainly with TRACE and SDO and 2) running Transverse Waves seen with CoMP. Results. We demonstrate that the observed period-damping time scaling law does provide information about the physical damping mechanism, if observations are collected from as wide as possible range of periods and a comparison with theory is performed in a statistical sense. The distribution of the ratio of damping time over period, i.e. the quality factor, has been derived analytically and fitted to the observations. A minimum value for the quality factor of 0.65 has been found. From this, a constraint linking the ranges of possible values for the density contrast and inhomogeneity layer thickness is obtained for Transverse loop oscillations. If the layer thickness is not constrained, then the density contrast is maximally equal to 3. For Transverse Waves seen by CoMP, it is found that the ratio of maximum to minimum values for these two parameters has to be less than 2.06. i.e. the sampled values for the layer thickness and Alfven travel time comes from a relatively narrow distribution. ´ Conclusions. Now that more and more Transverse loop oscillations have been analysed, a statistical approach to coronal seismology becomes possible. Using the observed data cloud restrictions in the loop parameter space of density contrast and inhomogeneity layer thickness are found and surprisingly for the running Waves narrow distributions for loop parameters have been found.
J Goree - One of the best experts on this subject based on the ideXlab platform.
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dispersion relations of longitudinal and Transverse Waves in two dimensional screened coulomb crystals
Physical Review E, 2002Co-Authors: S Nunomura, J Goree, Xiaogang Wang, A HattacharjeeAbstract:Dispersion relations of longitudinal and Transverse Waves in two-dimensional (2D) screened-Coulomb crystals were investigated. The Waves were excited in 2D crystals made from complex plasmas, i.e., dusty plasmas, by applying radiation pressure of laser light. The dependencies of the dispersion relation on the shielding parameter, the damping rate, and the wave propagation direction were experimentally measured. The measured dispersion relations agree reasonably with a recently developed theory, and the comparison yields the shielding parameter and the charge on particles.
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Transverse Waves in a two dimensional screened coulomb crystal dusty plasma
Physical Review Letters, 2000Co-Authors: S Nunomura, D Samsonov, J GoreeAbstract:Transverse shear Waves were observed experimentally in a two-dimensional screened Coulomb crystal. They were excited by applying a chopped laser beam to a 2D dusty plasma, i.e., a monolayer of charged microspheres levitated in a plasma. Measurements of the dispersion relation reveal an acoustic, i.e., nondispersive, character over the entire range of wave numbers measured, 0.2
A Hattacharjee - One of the best experts on this subject based on the ideXlab platform.
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dispersion relations of longitudinal and Transverse Waves in two dimensional screened coulomb crystals
Physical Review E, 2002Co-Authors: S Nunomura, J Goree, Xiaogang Wang, A HattacharjeeAbstract:Dispersion relations of longitudinal and Transverse Waves in two-dimensional (2D) screened-Coulomb crystals were investigated. The Waves were excited in 2D crystals made from complex plasmas, i.e., dusty plasmas, by applying radiation pressure of laser light. The dependencies of the dispersion relation on the shielding parameter, the damping rate, and the wave propagation direction were experimentally measured. The measured dispersion relations agree reasonably with a recently developed theory, and the comparison yields the shielding parameter and the charge on particles.
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longitudinal and Transverse Waves in yukawa crystals
Physical Review Letters, 2001Co-Authors: Xiaogang Wang, A HattacharjeeAbstract:A unified theoretical treatment is given of longitudinal (or compressional) and Transverse modes in Yukawa crystals, including the effects of damping. Dispersion relations are obtained for hexagonal lattices in two dimensions and bcc and fcc lattices in three dimensions. Theoretical predictions are compared with two recent experiments.
