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Fluting Modes in Transversely Nonuniform Solar Flux Tubes  

Roberto Soler   Submitted: 2017-11-23 03:49

Magnetohydrodynamic waves of different types are frequently observed in magnetic flux tubes of the solar atmosphere and are often modeled using simple models. In the standard flux tube model made of a straight uniform tube with an abrupt boundary, transverse wave modes are classified according to their azimuthal wavenumber, m. Sausage (m = 0) and kink (m = 1) modes produce pulsations of the cross section and transverse oscillations of tube axis, respectively. Both sausage and kink modes have been observed in the solar atmosphere. Fluting (m≥ 2) modes produce perturbations that are essentially confined around the boundary of the tube, i.e., they have a strong surface-like character. Unlike sausage and kink modes, the detection of fluting modes remains elusive. Here we show that the inclusion of transverse inhomogeneity in the flux tube model dramatically affects the properties of fluting modes. Even in a thin tube, kink and fluting modes are no longer degenerate in frequency when the tube has a smooth boundary. In addition, fluting modes become heavily damped by resonant absorption in a timescale shorter than the oscillation period. The perturbations loose their global shape and their distinctive surface-like appearance. As a consequence of that, we argue that nonuniform flux tubes with smooth boundaries may not be able to support fluting-like perturbations as coherent, global modes.

Authors: Roberto Soler
Projects: None

Publication Status: Published in ApJ
Last Modified: 2017-11-25 10:02
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Propagation of Torsional Alfvén Waves from the Photosphere to the Corona: Reflection, Transmission, and Heating in Expanding Flux Tubes  

Roberto Soler   Submitted: 2017-05-11 10:17

It has been proposed that Alfvén waves play an important role in the energy propagation through the solar atmospheric plasma and its heating. Here we theoretically investigate the propagation of torsional Alfvén waves in magnetic flux tubes expanding from the photosphere up to the low corona and explore the reflection, transmission, and dissipation of wave energy. We use a realistic variation of the plasma properties and the magnetic field strength with height. Dissipation by ion?neutral collisions in the chromosphere is included using a multifluid partially ionized plasma model. Considering the stationary state, we assume that the waves are driven below the photosphere and propagate to the corona, while they are partially reflected and damped in the chromosphere and transition region. The results reveal the existence of three different propagation regimes depending on the wave frequency: low frequencies are reflected back to the photosphere, intermediate frequencies are transmitted to the corona, and high frequencies are completely damped in the chromosphere. The frequency of maximum transmissivity depends on the magnetic field expansion rate and the atmospheric model, but is typically in the range of 0.04?0.3 Hz. Magnetic field expansion favors the transmission of waves to the corona and lowers the reflectivity of the chromosphere and transition region compared to the case with a straight field. As a consequence, the chromospheric heating due to ion?neutral dissipation systematically decreases when the expansion rate of the magnetic flux tube increases.

Authors: R. Soler, J. Terradas, R. Oliver, J. L. Ballester
Projects: None

Publication Status: Published in ApJ
Last Modified: 2017-05-18 11:32
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The role of Alfvén wave heating in solar prominences  

Roberto Soler   Submitted: 2016-05-23 23:58

Observations have shown that magnetohydrodynamic waves over a large frequency range are ubiquitous in solar prominences. The waves are probably driven by photospheric motions and may transport energy up to prominences suspended in the corona. Dissipation of wave energy can lead to heating of the cool prominence plasma, so contributing to the local energy balance within the prominence. Here we discuss the role of Alfvén wave dissipation as a heating mechanism for the prominence plasma. We consider a slab-like quiescent prominence model with a transverse magnetic field embedded in the solar corona. The prominence medium is modelled as a partially ionized plasma composed of a charged ion-electron single fluid and two separate neutral fluids corresponding to neutral hydrogen and neutral helium. Friction between the three fluids acts as a dissipative mechanism for the waves. The heating caused by externally-driven Alfvén waves incident on the prominence slab is analytically explored. We find that the dense prominence slab acts as a resonant cavity for the waves. The fraction of incident wave energy that is channelled into the slab strongly depends upon the wave period, P. Using typical prominence conditions, we obtain that wave energy trapping and associated heating are negligible when P ≳ 100 s, so that it is unlikely that those waves have a relevant influence on prominence energetics. When 1 s ≤sssim P ≤sssim 100 s the energy absorption into the slab shows several sharp and narrow peaks, that can reach up to 100%, when the incident wave frequency matches a cavity resonance of the slab. Wave heating is enhanced at those resonant frequencies. Conversely, when P ≤sssim 1 s cavity resonances are absent, but the waves are heavily damped by the strong dissipation. We estimate that wave heating may compensate for about 10% of radiative losses of the prominence plasma.

Authors: Roberto Soler, Jaume Terradas, Ramon Oliver, Jose Luis Ballester
Projects: None

Publication Status: Accepted in A&A
Last Modified: 2016-05-25 12:31
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Damped transverse oscillations of interacting coronal loops  

Roberto Soler   Submitted: 2015-09-06 23:47

Damped transverse oscillations of magnetic loops are routinely observed in the solar corona. This phenomenon is interpreted as standing kink magnetohydrodynamic waves, which are damped by resonant absorption owing to plasma inhomogeneity across the magnetic field. The periods and damping times of these oscillations can be used to probe the physical conditions of the coronal medium. Some observations suggest that interaction between neighboring oscillating loops in an active region may be important and can modify the properties of the oscillations compared to those of an isolated loop. Here we theoretically investigate resonantly damped transverse oscillations of interacting non-uniform coronal loops. We provide a semi-analytic method, based on the T-matrix theory of scattering, to compute the frequencies and damping rates of collective oscillations of an arbitrary configuration of parallel cylindrical loops. The effect of resonant damping is included in the T-matrix scheme in the thin boundary approximation. Analytic and numerical results in the specific case of two interacting loops are given as an application.

Authors: Roberto Soler and Manuel Luna
Projects: None

Publication Status: Accepted in A&A
Last Modified: 2015-09-08 05:18
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On the spatial scales of wave heating in the solar chromosphere  

Roberto Soler   Submitted: 2015-08-07 01:12

Dissipation of magnetohydrodynamic (MHD) wave energy has been proposed as a viable heating mechanism in the solar chromospheric plasma. Here, we use a simplified one-dimensional model of the chromosphere to theoretically investigate the physical processes and the spatial scales that are required for the efficient dissipation of Alfvén waves and slow magnetoacoustic waves. We consider the governing equations for a partially ionized hydrogen-helium plasma in the single-fluid MHD approximation and include realistic wave damping mechanisms that may operate in the chromosphere, namely Ohmic and ambipolar magnetic diffusion, viscosity, thermal conduction, and radiative losses. We perform an analytic local study in the limit of small amplitudes to approximately derive the lengthscales for critical damping and efficient dissipation of MHD wave energy. We find that the critical dissipation lengthscale for Alfvén waves depends strongly on the magnetic field strength and ranges from 10~m to 1 km for realistic field strengths. The damping of Alfvén waves is dominated by Ohmic diffusion for weak magnetic field and low heights in the chromosphere, and by ambipolar diffusion for strong magnetic field and medium/large heights in the chromosphere. Conversely, the damping of slow magnetoacoustic waves is less efficient, and spatial scales shorter than 10~m are required for critical damping. Thermal conduction and viscosity govern the damping of slow magnetoacoustic waves and play an equally important role at all heights. These results indicate that the spatial scales at which strong wave heating may work in the chromosphere are currently unresolved by observations.

Authors: Roberto Soler, Marc Carbonell, Jose Luis Ballester
Projects: None

Publication Status: Accepted in ApJ
Last Modified: 2015-08-10 11:13
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Magnetohydrodynamic kink waves in nonuniform solar flux tubes: phase mixing and energy cascade to small scales  

Roberto Soler   Submitted: 2015-02-15 23:57

Magnetohydrodynamic (MHD) kink waves are ubiquitously observed in the solar atmosphere. The propagation and damping of these waves may play relevant roles for the transport and dissipation of energy in the solar atmospheric medium. However, in the atmospheric plasma dissipation of transverse MHD wave energy by viscosity or resistivity needs very small spatial scales to be efficient. Here, we theoretically investigate the generation of small scales in nonuniform solar magnetic flux tubes due to phase mixing of MHD kink waves. We go beyond the usual approach based on the existence of a global quasi-mode that is damped in time due to resonant absorption. Instead, we use a modal expansion to express the MHD kink wave as a superposition of Alfvén continuum modes that are phase mixed as time evolves. The comparison of the two techniques evidences that the modal analysis is more physically transparent and describes both the damping of global kink motions and the building up of small scales due to phase mixing. In addition, we discuss that the processes of resonant absorption and phase mixing are intimately linked. They represent two aspects of the same underlying physical mechanism: the energy cascade from large scales to small scales due to naturally occurring plasma and/or magnetic field inhomogeneities. This process may provide the necessary scenario for efficient dissipation of transverse MHD wave energy in the solar atmospheric plasma.

Authors: Roberto Soler and Jaume Terradas
Projects: None

Publication Status: Accepted in ApJ
Last Modified: 2015-02-18 12:14
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Prominence seismology using the period ratio of transverse thread oscillations  

Roberto Soler   Submitted: 2015-01-22 05:29

The ratio of the period of the fundamental mode to that of the first overtone of kink oscillations, from here on the "period ratio", is a seismology tool that can be used to infer information about the spatial variation of density along solar magnetic flux tubes. The period ratio is 2 in longitudinally homogeneous thin tubes, but it differs from 2 due to longitudinal inhomogeneity. In this paper we investigate the period ratio in longitudinally inhomogeneous prominence threads and explore its implications for prominence seismology. We numerically solve the two-dimensional eigenvalue problem of kink oscillations in a model of a prominence thread. We take into account three nonuniform density profiles along the thread. In agreement with previous works that used simple piecewise constant density profiles, we find that the period ratio is larger than 2 in prominence threads. When the ratio of the central density to that at the footpoints is fixed, the period ratio depends strongly on the form of the density profile along the thread. The more concentrated the dense prominence plasma near the center of the tube, the larger the period ratio. However, the period ratio is found to be independent of the specific density profile when the spatially averaged density in the thread is the same for all the profiles. An empirical fit of the dependence of the period ratio on the average density is given and its use for prominence seismology is discussed.

Authors: R. Soler, M. Goossens, J. L. Ballester
Projects: None

Publication Status: Accepted in A&A
Last Modified: 2015-01-23 08:36
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Overdamped Alfvén waves due to ion-neutral collisions in the solar chromosphere  

Roberto Soler   Submitted: 2014-11-24 07:26

Alfvénic waves are ubiquitous in the solar atmosphere and their dissipation may play an important role in atmospheric heating. In the partially ionized solar chromosphere, collisions between ions and neutrals are an efficient dissipative mechanism for Alfvén waves with frequencies near the ion-neutral collision frequency. The collision frequency is proportional to the ion-neutral collision cross section for momentum transfer. Here, we investigate Alfvén wave damping as a function of height in a simplified chromospheric model and compare the results for two sets of collision cross sections, namely those of the classic hard-sphere model and those based on recent quantum-mechanical computations. We find important differences between the results for the two sets of cross sections. There is a critical interval of wavelengths for which impulsively excited Alfvén waves are overdamped as a result of the strong ion-neutral dissipation. The critical wavelengths are in the range from 1 km to 50 km for the hard-sphere cross sections, and from 1 m to 1 km for the quantum-mechanical cross sections. Equivalently, for periodically driven Alfvén waves there is an optimal frequency for which the damping is most effective. The optimal frequency varies from 1 Hz to 102 Hz for the hard-sphere cross sections, and from 102 Hz to 104 Hz for the quantum-mechanical cross sections. Future observations at sufficiently high spatial or temporal resolution may show the importance of high-frequency Alfvén waves for chromospheric heating. For instance, the Atacama Large Millimeter/submillimeter Array (ALMA) may be able to detect the critical wavelengths and optimal frequencies and so to test the effective collision cross section in the chromospheric plasma.

Authors: R. Soler, J. L. Ballester, T. V. Zaqarashvili
Projects: None

Publication Status: Accepted in A&A
Last Modified: 2014-11-24 07:26
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The behavior of transverse waves in nonuniform solar flux tubes. II. Implications for coronal loop seismology  

Roberto Soler   Submitted: 2013-12-19 04:12

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 to 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 to the period and damping time, and its 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.

Authors: Roberto Soler, Marcel Goossens, Jaume Terradas, Ramon Oliver
Projects: None

Publication Status: Accepted for publication in ApJ
Last Modified: 2013-12-19 07:43
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Magnetoacoustic waves in a partially ionized two-fluid plasma  

Roberto Soler   Submitted: 2013-09-30 11:57

Compressible disturbances propagate in a plasma in the form of magnetoacoustic waves driven by both gas pressure and magnetic forces. In partially ionized plasmas the dynamics of ionized and neutral species are coupled due to ion-neutral collisions. As a consequence, magnetoacoustic waves propagating through a partially ionized medium are affected by the ion-neutral coupling. The degree to which the behavior of the classic waves is modified depends on the physical properties of the various species and on the relative value of the wave frequency compared to the ion-neutral collision frequency. Here, we perform a comprehensive theoretical investigation of magnetoacoustic wave propagation in a partially ionized plasma using the two-fluid formalism. We consider an extensive range of values for the collision frequency, ionization ratio, and plasma eta, so that the results are applicable to a wide variety of astrophysical plasmas. We determine the modification of the wave frequencies and study the frictional damping due to ion-neutral collisions. Approximate analytic expressions to the frequencies are given in the limit case of strongly coupled ions and neutrals, while numerically obtained dispersion diagrams are provided for arbitrary collision frequencies. In addition, we discuss the presence of cutoffs in the dispersion diagrams that constrain wave propagation for certain combinations of parameters. A specific application to propagation of compressible waves in the solar chromosphere is given.

Authors: R. Soler, M. Carbonell, J. L. Ballester
Projects: None

Publication Status: Accepted for publication in ApJ Supplement Series
Last Modified: 2013-10-01 21:52
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The behavior of transverse waves in nonuniform solar flux tubes. I. Comparison of ideal and resistive results  

Roberto Soler   Submitted: 2013-09-16 09:07

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 are 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 Alfvén 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.

Authors: R. Soler, M. Goossens, J. Terradas, R. Oliver
Projects: None

Publication Status: Accepted for publication in ApJ
Last Modified: 2013-09-16 11:32
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Alfvén waves in a partially ionized two-fluid plasma  

Roberto Soler   Submitted: 2013-03-19 02:09

Alfvén waves are a particular class of magnetohydrodynamic waves relevant in many astrophysical and laboratory plasmas. In partially ionized plasmas the dynamics of Alfvén waves is affected by the interaction between ionized and neutral species. Here we study Alfvén waves in a partially ionized plasma from the theoretical point of view using the two-fluid description. We consider that the plasma is composed of an ion-electron fluid and a neutral fluid, which interact by means of particle collisions. To keep our investigation as general as possible we take the neutral-ion collision frequency and the ionization degree as free parameters. First, we perform a normal mode analysis. We find the modification due to neutral-ion collisions of the wave frequencies and study the temporal and spatial attenuation of the waves. In addition, we discuss the presence of cut-off values of the wavelength that constrain the existence of oscillatory standing waves in weakly ionized plasmas. Later, we go beyond the normal mode approach and solve the initial-value problem in order to study the time-dependent evolution of the wave perturbations in the two fluids. An application to Alfvén waves in the low solar atmospheric plasma is performed and the implication of partial ionization for the energy flux is discussed.

Authors: R. Soler, M. Carbonell, J. L. Ballester, J. Terradas
Projects: None

Publication Status: Accepted in ApJ
Last Modified: 2013-03-19 09:39
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Effect of partial ionization on wave propagation in solar magnetic flux tubes  

Roberto Soler   Submitted: 2013-01-23 03:44

Observations show that waves are ubiquitous in the solar atmosphere and may play an important role for plasma heating. The study of waves in the solar corona is usually based on linear ideal magnetohydrodynamics (MHD) for a fully ionized plasma. However, the plasma in the photosphere and the chromosphere is only partially ionized. Here we investigate theoretically the impact of partial ionization on MHD wave propagation in cylindrical flux tubes in the two-fluid model. We derive the general dispersion relation that takes into account the effects of neutral-ion collisions and the neutral gas pressure. We take the neutral-ion collision frequency as an arbitrary parameter. Particular results for transverse kink modes and slow magnetoacoustic modes are shown. We find that the wave frequencies only depend on the properties of the ionized fluid when the neutral-ion collision frequency is much lower that the wave frequency. For high collision frequencies realistic of the solar atmosphere ions and neutrals behave as a single fluid with an effective density corresponding to the sum of densities of both fluids and an effective sound velocity computed as the average of the sound velocities of ions and neutrals. The MHD wave frequencies are modified accordingly. The neutral gas pressure can be neglected when studying transverse kink waves but it has to be taken into account for a consistent description of slow magnetoacoustic waves. The MHD waves are damped due to neutral-ion collisions. The damping is most efficient when the wave frequency and the collision frequency are of the same order of magnitude. For high collision frequencies slow magnetoacoustic waves are more efficiently damped than transverse kink waves. In addition, we find the presence of cut-offs for certain combinations of parameters that cause the waves to become non-propagating.

Authors: R. Soler, A. J. Diaz, J. L. Ballester, M. Goossens
Projects: None

Publication Status: Accepted for publication in A&A
Last Modified: 2013-01-23 12:18
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Analytic approximate seismology of propagating MHD waves in the solar corona  

Roberto Soler   Submitted: 2012-10-09 23:57

Observations show that propagating magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. The technique of MHD seismology uses the wave observations combined with MHD wave theory to indirectly infer physical parameters of the solar atmospheric plasma and magnetic field. Here we present an analytical seismological inversion scheme for propagating MHD waves. This scheme uses in a consistent manner the observational information on wavelengths and damping lengths, along with observed values of periods or phase velocities, and is based on approximate asymptotic expressions for the theoretical values of wavelengths and damping lengths. The applicability of the inversion scheme is discussed and an example is given.

Authors: M. Goossens, R. Soler, I. Arregui, J. Terradas
Projects: None

Publication Status: Accepted in ApJ
Last Modified: 2012-10-10 09:03
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Damped kink oscillations of flowing prominence threads  

Roberto Soler   Submitted: 2012-09-18 04:27

Transverse oscillations of thin threads in solar prominences are frequently reported in high-resolution observations. Two typical features of the observations are that the oscillations are damped in time and that simultaneous mass flows along the threads are detected. Flows cause the dense threads to move along the prominence magnetic structure while the threads are oscillating. The oscillations have been interpreted in terms of standing magnetohydrodynamic (MHD) kink waves of the magnetic flux tubes which support the threads. The damping is most likely due to resonant absorption caused by plasma inhomogeneity. The technique of seismology uses the observations combined with MHD wave theory to estimate prominence physical parameters. This paper presents a theoretical study of the joint effect of flow and resonant absorption on the amplitude of standing kink waves in prominence threads. We find that flow and resonant absorption can either be competing effects on the amplitude or both can contribute to damp the oscillations depending on the instantaneous position of the thread within the prominence magnetic structure. The amplitude profile deviates from the classic exponential profile of resonantly damped kink waves in static flux tubes. Flow also introduces a progressive shift of the oscillation period compared to the static case, although this effect is in general of minor importance. We test the robustness of seismological estimates by using synthetic data aiming to mimic real observations. The effect of the thread flow can significantly affect the estimation of the transverse inhomogeneity length scale. The presence of random background noise adds uncertainty to this estimation. Caution needs to be paid to the seismological estimates that do not take the influence of flow into account.

Authors: R. Soler, M. S. Ruderman, M. Goossens
Projects: None

Publication Status: Accepted in A&A
Last Modified: 2012-09-18 10:51
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Surface Alfvén waves in solar flux tubes  

Roberto Soler   Submitted: 2012-05-07 03:28

Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. Alfvén waves and magneto-sonic waves are particular classes of MHD waves. These wave modes are clearly different and have pure properties in uniform plasmas of infinite extent only. Due to plasma non-uniformity MHD waves have mixed properties and cannot be classified as pure Alfvén or magneto-sonic waves. However, vorticity is a quantity unequivocally related to Alfvén waves as compression is for magneto-sonic waves. Here, we investigate MHD waves superimposed on a one-dimensional non-uniform straight cylinder with constant magnetic field. For a piecewise constant density profile we find that the fundamental radial modes of the non-axisymmetric waves have the same properties as surface Alfvén waves at a true discontinuity in density. Contrary to the classic Alfvén waves in a uniform plasma of infinite extent, vorticity is zero everywhere except at the cylinder boundary. If the discontinuity in density is replaced with a continuous variation of density, vorticity is spread out over the whole interval with non-uniform density. The fundamental radial modes of the non-axisymmetric waves do not need compression to exist unlike the radial overtones. In thin magnetic cylinders the fundamental radial modes of the non-axisymmetric waves with phase velocities between the internal and the external Alfvén velocities can be considered as surface Alfvén waves. On the contrary, the radial overtones can be related to fast-like magneto-sonic modes.

Authors: Goossens, M.; Andries, J.; Soler, R.; Van Doorsselaere, T.; Arregui, I.; Terradas, J.
Projects: None

Publication Status: Accepted in ApJ
Last Modified: 2012-05-07 13:36
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Kelvin-Helmholtz instability in partially ionized compressible plasmas  

Roberto Soler   Submitted: 2012-02-21 04:58

The Kelvin-Helmholtz Instability (KHI) has been observed in the solaratmosphere. Ion-neutral collisionsmay play a relevant role for the growth rate and evolution of the KHIin solar partially ionized plasmas asin, e.g., solar prominences. Here, we investigate the linear phase ofthe KHI at an interface between twopartially ionized magnetized plasmas in the presence of a shear flow.The effects of ion-neutral collisions andcompressibility are included in the analysis. We obtain the dispersionrelation of the linear modes and performparametric studies of the unstable solutions. We find that in theincompressible case the KHI is present for anyvelocity shear regardless the value of the collision frequency. In thecompressible case, the domain of instabilitydepends strongly on the plasma parameters, specially the collisionfrequency and the density contrast. For highcollision frequencies and low density contrasts the KHI is present forsuper-Alfvénic velocity shear only. Forhigh density contrasts the threshold velocity shear can be reduced tosub-Alfvénic values. For the particularcase of turbulent plumes in prominences, we conclude thatsub-Alfvénic flow velocities can trigger the KHIthanks to the ion-neutral coupling.

Authors: R. Soler, A. J. Diaz, J. L. Ballester, M. Goossens
Projects: None

Publication Status: Accepted for publication in ApJ
Last Modified: 2012-02-21 10:24
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Stability of thermal modes in cool prominence plasmas  

Roberto Soler   Submitted: 2012-01-24 04:12

Prominences or filaments are cool clouds of partially ionized plasmalivingin the solar corona. Ground- and space-based observations haveconfirmed the presenceof oscillatory motions in prominences and they have been interpretedin termsof magnetohydrodynamic (MHD) waves. Existing observational evidencepoints outthat these oscillatory motions are damped in short spatial andtemporal scales bysome still not well known physical mechanism(s). Since prominences arepartiallyionized plasmas, a potential mechanism able to damp these oscillationscould beion-neutral collisions. Here, we will review the work done on theeffects of partialionization on MHD waves in prominence plasmas.

Authors: R. Soler, J. L. Ballester, S. Parenti
Projects: None

Publication Status: Accepted for publication in A&A
Last Modified: 2012-01-24 11:24
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Magnetohydrodynamic Waves in Partially Ionized Prominence Plasmas  

Roberto Soler   Submitted: 2012-01-19 03:14

Prominences or filaments are cool clouds of partially ionized plasmalivingin the solar corona. Ground- and space-based observations haveconfirmed the presenceof oscillatory motions in prominences and they have been interpretedin termsof magnetohydrodynamic (MHD) waves. Existing observational evidencepoints outthat these oscillatory motions are damped in short spatial andtemporal scales bysome still not well known physical mechanism(s). Since prominences arepartiallyionized plasmas, a potential mechanism able to damp these oscillationscould beion-neutral collisions. Here, we will review the work done on theeffects of partialionization on MHD waves in prominence plasmas.

Authors: Roberto Soler, Jose Luis Ballester
Projects: None

Publication Status: Review paper to appear in Astrophysics and Space Science Proceedings
Last Modified: 2012-01-19 13:26
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Resonant Alfvén waves in partially ionized plasmas of the solar atmosphere  

Roberto Soler   Submitted: 2011-11-18 03:15

Context. Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. In magnetic waveguides resonant absorption due to plasma inhomogeneity naturally transfers wave energy from large-scale motions to small-scale motions. In the cooler parts of the solar atmosphere as, e.g., the chromosphere, effects due to partial ionization may be relevant for wave dynamics and heating. Aims. We study resonant Alfvén waves in partially ionized plasmas. Methods. We use the multifluid equations in the cold plasma approximation. We investigate propagating resonant MHD waves in partially ionized flux tubes. We use approximate analytical theory based on normal modes in the thin tube and thin boundary approximations along with numerical eigenvalue computations. Results. We find that the jumps of the wave perturbations across the resonant layer are the same as in fully ionized plasmas. The damping length due to resonant absorption is inversely proportional to the frequency, while that due to ion-neutral collisions is inversely proportional to the square of the frequency. For observed frequencies in the solar atmosphere, the amplitude of MHD kink waves is more efficiently damped by resonant absorption than by ion-neutral collisions. Conclusions. Most of the energy carried by chromospheric kink waves is converted into localized azimuthal Alfvén waves that can deposit energy in the coronal medium. The dissipation of wave energy in the chromosphere due to ion-neutral collisions is only effective for high-frequency waves. The chromosphere acts as a filter for kink waves with periods shorter than 10 s.

Authors: R. Soler, J. Andries, and M. Goossens
Projects: None

Publication Status: Accepted for publication in A&A
Last Modified: 2011-11-18 09:30
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Abstracts by Author
Fluting Modes in Transversely Nonuniform Solar Flux Tubes
Propagation of Torsional Alfv?n Waves from the Photosphere to the Corona: Reflection, Transmission, and Heating in Expanding Flux Tubes
The role of Alfv?n wave heating in solar prominences
Damped transverse oscillations of interacting coronal loops
On the spatial scales of wave heating in the solar chromosphere
Magnetohydrodynamic kink waves in nonuniform solar flux tubes: phase mixing and energy cascade to small scales
Prominence seismology using the period ratio of transverse thread oscillations
Overdamped Alfven waves due to ion-neutral collisions in the solar chromosphere
The behavior of transverse waves in nonuniform solar flux tubes. II. Implications for coronal loop seismology
Magnetoacoustic waves in a partially ionized two-fluid plasma
The behavior of transverse waves in nonuniform solar flux tubes. I. Comparison of ideal and resistive results
Alfven waves in a partially ionized two-fluid plasma
Effect of partial ionization on wave propagation in solar magnetic flux tubes
Analytic approximate seismology of propagating MHD waves in the solar corona
Damped kink oscillations of flowing prominence threads
Surface Alfven waves in solar flux tubes
Kelvin-Helmholtz instability in partially ionized compressible plasmas
Stability of thermal modes in cool prominence plasmas
Magnetohydrodynamic Waves in Partially Ionized Prominence Plasmas
Resonant Alfven waves in partially ionized plasmas of the solar atmosphere
Kink oscillations of flowing threads in solar prominences
Resonantly Damped Propagating Kink Waves in Longitudinally Stratified Solar Waveguides
Spatial Damping of Propagating Kink Waves Due to Resonant Absorption: Effect of Background Flow
The Thermal Instability of Solar Prominence Threads
Spatial Damping of Propagating Kink Waves in Prominence Threads
Damping of Magnetohydrodynamic Waves in Solar Prominence Fine Structures
Seismology of Standing Kink Oscillations of Solar Prominence Fine Structures
Kelvin-Helmholtz instability in coronal magnetic flux tubes due to azimuthal shear flows
Time damping of non-adiabatic magnetohydrodynamic waves in a partially ionized prominence plasma: Effect of helium
Resonantly Damped Kink Magnetohydrodynamic Waves in a Partially Ionized Filament Thread
Magnetohydrodynamic Waves in a Partially Ionized Filament Thread
Damping of filament thread oscillations: effect of the slow continuum
Propagation of nonadiabatic magnetoacoustic waves in a threaded prominence with mass flows
Subject will be restored when possible
Subject will be restored when possible
Subject will be restored when possible
The effect of the solar corona on the attenuation of small-amplitude prominence oscillations. I. Longitudinal magnetic field

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MSU Solar Physics.
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Max Millennium Flare Catalog

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