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* News 04/04/20 * The archive is using a new backend database. This has thrown up a few SQL errors in the last few days. If you have any issues please email adavey@nso.edu with either the number of eprint you are trying to edit or a link to your preprint.

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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Kink oscillations of flowing threads in solar prominences  

Roberto Soler   Submitted: 2011-06-21 04:44

Recent observations by Hinode/SOT show that MHD waves and mass flows are simultaneously present in the fine structure of solar prominences. We investigate standing kink magnetohydrodynamic (MHD) waves in flowing prominence threads from a theoretical point of view. We model a prominence fine structure as a cylindrical magnetic tube embedded in the solar corona with its ends line-tied in the photosphere. The magnetic cylinder is composed of a region with dense prominence plasma, which is flowing along the magnetic tube, whereas the rest of the flux tube is occupied by coronal plasma. We use the WKB approximation to obtain analytical expressions for the period and the amplitude of the fundamental mode as functions of the flow velocity. In addition, we solve the full problem numerically by means of time-dependent simulations. We find that both the period and the amplitude of the standing MHD waves vary in time as the prominence thread flows along the magnetic structure. The fundamental kink mode is a good description for the time-dependent evolution of the oscillations, and the analytical expressions in the WKB approximation are in agreement with the full numerical results. The presence of flow modifies the period of the oscillations with respect to the static case. However, for realistic flow velocities this effect might fall within the error bars of the observations. The variation of the amplitude due to the flow leads to apparent damping or amplification of the oscillations, which could modify the real rate of attenuation caused by an additional damping mechanism.

Authors: Roberto Soler and Marcel Goossens
Projects: None

Publication Status: Accepted in A&A
Last Modified: 2011-06-21 13:47
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Resonantly Damped Propagating Kink Waves in Longitudinally Stratified Solar Waveguides  

Roberto Soler   Submitted: 2011-05-03 03:31

It has been shown that resonant absorption is a robust physical mechanism to explain the observed damping of magnetohydrodynamic (MHD) kink waves in the solar atmosphere due to naturally occurring plasma inhomogeneity in the direction transverse to the direction of the magnetic field. Theoretical studies of this damping mechanism were greatly inspired by the first observations of post-flare standing kink modes in coronal loops using the Transition Region And Coronal Explorer (TRACE). More recently, these studies have been extended to explain the attenuation of propagating coronal kink waves observed by the Coronal Multi-Channel Polarimeter (CoMP). In the present study, for the first time we investigate the properties of propagating kink waves in solar waveguides including the effects of both longitudinal and transverse plasma inhomogeneity. Importantly, it is found that the wavelength is only dependent on the longitudinal stratification and the amplitude is simply a product of the two effects. In light of these results the advancement of solar atmospheric magnetoseismology by exploiting high spatial/temporal resolution observations of propagating kink waves in magnetic waveguides to determine the length scales of the plasma inhomogeneity along and transverse to the direction of the magnetic field is discussed.

Authors: Roberto Soler, Jaume Terradas, Gary Verth, Marcel Goossens
Projects: None

Publication Status: Accepted for publication in ApJ
Last Modified: 2011-05-03 08:46
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Spatial Damping of Propagating Kink Waves Due to Resonant Absorption: Effect of Background Flow  

Roberto Soler   Submitted: 2011-04-12 02:44

Observations show the ubiquitous presence of propagating magnetohydrodynamic (MHD) kink waves in the solar atmosphere. Waves and flows are often observed simultaneously. Due to plasma inhomogeneity in the perpendicular direction to the magnetic field, kink waves are spatially damped by resonant absorption. The presence of flow may affect the wave spatial damping. Here, we investigate the effect of longitudinal background flow on the propagation and spatial damping of resonant kink waves in transversely nonuniform magnetic flux tubes. We combine approximate analytical theory with numerical investigation. The analytical theory uses the thin tube (TT) and thin boundary (TB) approximations to obtain expressions for the wavelength and the damping length. Numerically, we verify the previously obtained analytical expressions by means of the full solution of the resistive MHD eigenvalue problem beyond the TT and TB approximations. We find that the backward and forward propagating waves have different wavelengths and are damped on length scales that are inversely proportional to the frequency as in the static case. However, the factor of proportionality depends on the characteristics of the flow, so that the damping length differs from its static analogue. For slow, sub-Alfvénic flows the backward propagating wave gets damped on a shorter length scale than in the absence of flow, while for the forward propagating wave the damping length is longer. The different properties of the waves depending on their direction of propagation with respect to the background flow may be detected by the observations and may be relevant for seismological applications.

Authors: Roberto Soler, Jaume Terradas, and Marcel Goossens
Projects: None

Publication Status: Accepted for publication in ApJ
Last Modified: 2011-04-12 08:45
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The Thermal Instability of Solar Prominence Threads  

Roberto Soler   Submitted: 2011-02-14 05:18

The fine structure of solar prominences and filaments appears as thin and long threads in high-resolution images. In Hα observations of filaments, some threads can be observed for only 5 - 20 minutes before they seem to fade and eventually disappear, suggesting that these threads may have very short lifetimes. The presence of an instability might be the cause of this quick disappearance. Here, we study the thermal instability of prominence threads as an explanation of their sudden disappearance from Hα observations. We model a prominence thread as a magnetic tube with prominence conditions embedded in a coronal environment. We assume a variation of the physical properties in the transverse direction, so that the temperature and density continuously change from internal to external values in an inhomogeneous transitional layer representing the particular prominence-corona transition region (PCTR) of the thread. We use the nonadiabatic and resistive magnetohydrodynamic equations, which include terms due to thermal conduction parallel and perpendicular to the magnetic field, radiative losses, heating, and magnetic diffusion. We combine both analytical and numerical methods to study linear perturbations from the equilibrium state, focusing on unstable thermal solutions. We find that thermal modes are unstable in the PCTR for temperatures higher than 80,000 K, approximately. These modes are related to temperature disturbances that can lead to changes in the equilibrium due to rapid plasma heating or cooling. For typical prominence parameters, the instability time scale is of the order of a few minutes and is independent of the form of the temperature profile within the PCTR of the thread. This result indicates that thermal instability may play an important role for the short lifetimes of threads in the observations.

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

Publication Status: Accepted for publication in ApJ
Last Modified: 2011-02-14 08:43
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Spatial Damping of Propagating Kink Waves in Prominence Threads  

Roberto Soler   Submitted: 2010-09-27 03:07

Transverse oscillations and propagating waves are frequently observed in threads of solar prominences/filaments and have been interpreted as kink magnetohydrodynamic (MHD) modes. We investigate the spatial damping of propagating kink MHD waves in transversely nonuniform and partially ionized prominence threads. Resonant absorption and ion-neutral collisions (Cowling's diffusion) are the damping mechanisms taken into account. The dispersion relation of resonant kink waves in a partially ionized magnetic flux tube is numerically solved by considering prominence conditions. Analytical expressions of the wavelength and damping length as functions of the kink mode frequency are obtained in the Thin Tube and Thin Boundary approximations. For typically reported periods of thread oscillations, resonant absorption is an efficient mechanism for the kink mode spatial damping, while ion-neutral collisions have a minor role. Cowling's diffusion dominates both the propagation and damping for periods much shorter than those observed. Resonant absorption may explain the observed spatial damping of kink waves in prominence threads. The transverse inhomogeneity length scale of the threads can be estimated by comparing the observed wavelengths and damping lengths with the theoretically predicted values. However, the ignorance of the form of the density profile in the transversely nonuniform layer introduces inaccuracies in the determination of the inhomogeneity length scale.

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

Publication Status: Submitted in ApJ
Last Modified: 2010-09-27 13:13
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Damping of Magnetohydrodynamic Waves in Solar Prominence Fine Structures  

Roberto Soler   Submitted: 2010-08-23 06:45

High-resolution observations of solar filaments and prominences reveal that these large-scale coronal structures are formed by a myriad of long and thin ribbons, here called threads, which are piled up to form the prominence body. Evidences suggest that these fine structures are magnetic flux tubes anchored in the solar photosphere, which are partially filled with the cool and dense prominence material. Individual and collective oscillations of prominence and filament fine structures are frequently reported by means of oscillatory variations in Doppler signals and spectral line intensity. Common features of these observations are that the reported oscillatory periods are usually in a narrow range between 2 and 10 minutes, that the velocity amplitudes are smaller than 3 km s-1, and that the oscillations seem to be strongly damped after a few periods. Typically, the ratio of the damping time, tD, to the period, P, is tD/P < 10. While the oscillations have been interpreted in the context of the magnetohydrodynamic (MHD) theory, i.e., in terms of the MHD normal modes supported by the filament thread body and/or propagating MHD waves, the mechanism or mechanisms responsible for the damping are not well-known and a comparative study between different damping mechanisms is needed. In this Thesis, we study the efficiency of several physical mechanisms for the damping of MHD oscillations in prominence fine structures. Both individual and collective oscillations of threads are analyzed. We model a filament thread as a straight cylindrical magnetic flux tube with prominence conditions, embedded in a magnetized environment representing the solar coronal medium. The basic MHD equations are applied to the model and contain non-ideal terms accounting for effects as, e.g., non-adiabatic mechanisms, magnetic diffusion, ion-neutral collisions, etc., that may be of relevance in prominence plasmas and whose role on the damping of the oscillations is assessed. Our method combines analytical treatments along with numerical computations to obtain the frequency and the perturbations of the linear MHD modes. Among the studied mechanisms, we find that the most efficient one for the damping of transverse thread oscillations, interpreted as kink MHD modes, is the process of resonant absorption in the Alfvén continuum. The efficiency of resonant absorption is independent of the plasma ionization degree and is consistent with the reported values of tD/P. Thermal effects, as well as magnetic diffusion, are irrelevant for the damping of transverse oscillations. Regarding longitudinal oscillations, i.e., slow MHD modes, radiative losses from the prominence plasma and ion-neutral collisions are the processes that provide the smallest damping times. Their combined effect causes an efficient attenuation of slow modes in filament threads, with tD/P compatible with the observed values. Finally, Alfvén waves are also investigated, and we obtain that they are damped by ion-neutral collisions. However, the damping of Alfvén waves is not very efficient because the theoretical damping times are between one and two orders of magnitude larger than the corresponding periods. All these conclusions apply for both individual and collective oscillations of threads.

Authors: Roberto Soler
Projects: None

Publication Status: PhD Thesis. University of the Balearic Islands.
Last Modified: 2010-08-23 12:55
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Seismology of Standing Kink Oscillations of Solar Prominence Fine Structures  

Roberto Soler   Submitted: 2010-07-13 03:55

Damped transverse oscillations of solar prominence fine structures are frequently reported and have been interpreted as kink magnetohydrodynamic (MHD) modes. Here, we investigate standing kink MHD oscillations in a prominence fine structure. Our model is composed of a magnetic tube only partially filled with the prominence material, while the coronal plasma occupies both the rest of the tube and the external medium. Ion-neutral collisions and resonant absorption are the considered damping mechanisms. Approximate analytical expressions of the period, the damping time, and the ratio of the damping time to the period are derived for the fundamental kink mode. A parametric study is performed by numerically solving the full dispersion relation. We find that the dominant damping mechanism is resonant absorption, which provides realistic damping ratios, whereas ion-neutral collisions are irrelevant for the damping. The values of the damping ratio are independent of both the prominence thread length and its position within the magnetic tube, and coincide with the values for a tube fully filled with the prominence plasma. The implications of our results in the context of the MHD seismology technique are discussed, pointing out that the reported short-period (2 - 10 min) and short-wavelength (700 - 8,000 km) thread oscillations may not be consistent with a standing mode interpretation and could be related to propagating waves. Finally, we show that the inversion of some prominence physical parameters, e.g., Alfvén speed, magnetic field strength, transverse inhomogeneity length-scale, etc., is possible using observationally determined values of the period and damping time of the oscillations along with the analytical approximations of these quantities.

Authors: R. Soler, I. Arregui, R. Oliver, and J. L. Ballester
Projects: None

Publication Status: Submitted in ApJ
Last Modified: 2010-07-13 12:29
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Kelvin-Helmholtz instability in coronal magnetic flux tubes due to azimuthal shear flows  

Roberto Soler   Submitted: 2009-12-21 04:56

Transverse oscillations of coronal loops are often observed and have been theoretically interpreted as kink magnetohydrodynamic (MHD) modes. Numerical simulations by Terradas et al. (2008, ApJ 687, L115) suggest that shear flows generated at the loop boundary during kink oscillations could give rise to a Kelvin-Helmholtz instability (KHI). Here, we investigate the linear stage of the KHI in a cylindrical magnetic flux tube in the presence of azimuthal shear motions. We consider the basic, linearized MHD equations in the beta = 0 approximation, and apply them to a straight and homogeneous cylindrical flux tube model embedded in a coronal environment. Azimuthal shear flows with a sharp jump of the velocity at the cylinder boundary are included in the model. We obtain an analytical expression for the dispersion relation of the unstable MHD modes supported by the configuration, and compute analytical approximations of the critical velocity shear and the KHI growth rate in the thin tube limit. A parametric study of the KHI growth rates is performed by numerically solving the full dispersion relation. We find that fluting-like modes can develop a KHI in time-scales comparable to the period of kink oscillations of the flux tube. The KHI growth rates increase with the value of the azimuthal wavenumber and decrease with the longitudinal wavenumber. However, the presence of a small azimuthal component of the magnetic field can suppress the KHI. Azimuthal motions related to kink oscillations of untwisted coronal loops may trigger a KHI, but this phenomenon has not been observed to date. We propose that the azimuthal component of the magnetic field is responsible for suppressing the KHI in a stable coronal loop. The required twist is small enough to prevent the development of the pinch instability.

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

Publication Status: Submitted in ApJ
Last Modified: 2009-12-21 12:27
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Time damping of non-adiabatic magnetohydrodynamic waves in a partially ionized prominence plasma: Effect of helium  

Roberto Soler   Submitted: 2009-10-16 02:51

Prominences are partially ionized, magnetized plasmas embedded in the solar corona. Damped oscillations and propagating waves are commonly observed. These oscillations have been interpreted in terms of magnetohydrodynamic (MHD) waves. Ion-neutral collisions and non-adiabatic effects (radiation losses and thermal conduction) have been proposed as damping mechanisms. We study the effect of the presence of helium on the time damping of non-adiabatic MHD waves in a plasma composed by electrons, protons, neutral hydrogen, neutral helium (He I), and singly ionized helium (He II) in the single-fluid approximation. The dispersion relation of linear non-adiabatic MHD waves in a homogeneous, unbounded, and partially ionized prominence medium is derived. The period and the damping time of Alfvén, slow, fast, and thermal waves are computed. A parametric study of the ratio of the damping time to the period with respect to the helium abundance is performed. The efficiency of ion-neutral collisions as well as thermal conduction is increased by the presence of helium. However, if realistic abundances of helium in prominences (~10%) are considered, this effect has a minor influence on the wave damping. The presence of helium can be safely neglected in studies of MHD waves in partially ionized prominence plasmas.

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

Publication Status: Research note submitted in A&A
Last Modified: 2009-10-16 08:54
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Resonantly Damped Kink Magnetohydrodynamic Waves in a Partially Ionized Filament Thread  

Roberto Soler   Submitted: 2009-09-22 02:43

Transverse oscillations of solar filament and prominence threads have been frequently reported. These oscillations have the common features of being of short period (2-10 min) and being damped after a few periods. Kink magnetohydrodynamic (MHD) wave modes have been proposed as responsible for the observed oscillations, whereas resonant absorption in the Alfvén continuum and ion-neutral collisions are the best candidates to be the damping mechanisms. Here, we study both analytically and numerically the time damping of kink MHD waves in a cylindrical, partially ionized filament thread embedded in a coronal environment. The thread model is composed of a straight and thin, homogeneous filament plasma, with a transverse inhomogeneous transitional layer where the plasma physical properties vary continuously from filament to coronal conditions. The magnetic field is homogeneous and parallel to the thread axis. We find that the kink mode is efficiently damped by resonant absorption for typical wavelengths of filament oscillations, the damping times being compatible with the observations. Partial ionization does not affect the process of resonant absorption, and the filament plasma ionization degree is only important for the damping for wavelengths much shorter than those observed. To our knowledge, this is the first time that the phenomenon of resonant absorption is studied in a partially ionized plasma.

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

Publication Status: Submitted in ApJ
Last Modified: 2009-09-22 07:39
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Magnetohydrodynamic Waves in a Partially Ionized Filament Thread  

Roberto Soler   Submitted: 2009-04-21 03:56

Oscillations and propagating waves are commonly seen in high-resolution observations of filament threads, i.e., the fine-structures of solar filaments/prominences. Since the temperature of prominences is typically of the order of 104 K, the prominence plasma is only partially ionized. In this paper, we study the effect of neutrals on the wave propagation in a filament thread modeled as a partially ionized homogeneous magnetic flux tube embedded in an homogeneous and fully ionized coronal plasma. Ohmic and ambipolar magnetic diffusion are considered in the basic resistive MHD equations. We numerically compute the eigenfrequencies of kink, slow, and Alfvén linear MHD modes, and obtain analytical approximations in some cases. We find that the existence of propagating modes is constrained by the presence of critical values of the longitudinal wavenumber. In particular, the lower and upper frequency cut-offs of kink and Alfvén waves owe their existence to magnetic diffusion parallel and perpendicular to magnetic field lines, respectively. The slow mode only has a lower frequency cut-off, which is caused by perpendicular magnetic diffusion and is significantly affected by the ionization degree. In addition, ion-neutral collisions is the most efficient damping mechanism for short wavelengths while ohmic diffusion dominates in the long-wavelength regime.

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

Publication Status: Submitted in ApJ
Last Modified: 2009-04-21 08:42
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Damping of filament thread oscillations: effect of the slow continuum  

Roberto Soler   Submitted: 2009-02-03 11:14

Transverse oscillations of small amplitude are commonly seen in high-resolution observations of filament threads, i.e. the fine-structures of solar filaments/prominences, and are typically damped in a few periods. Kink wave modes supported by the thread body offer a consistent explanation of these observed oscillations. Among the proposed mechanisms to explain the kink mode damping, resonant absorption in the Alfvén continuum seems to be the most efficient as it produces damping times of about 3 periods. However, for a nonzero-beta plasma and typical prominence conditions, the kink mode is also resonantly coupled to slow (or cusp) continuum modes, which could reduce further the damping time. In this Letter, we explore for the first time both analytically and numerically the effect of the slow continuum on the damping of transverse thread oscillations. The thread model is composed of a homogeneous and straight cylindrical plasma, an inhomogeneous transitional layer, and the homogeneous coronal plasma. We find that the damping of the kink mode due to the slow resonance is much less efficient than that due to the Alfvén resonance.

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

Publication Status: Submitted in ApJL
Last Modified: 2009-02-04 08:44
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Propagation of nonadiabatic magnetoacoustic waves in a threaded prominence with mass flows  

Roberto Soler   Submitted: 2008-09-30 02:58

High resolution observations of solar filaments suggest the presence of groups of prominence threads, i.e. the fine-structures of prominences, which oscillate coherently (in phase). In addition, mass flows along threads have been often observed. Here, we investigate the effect of mass flows on the collective fast and slow nonadiabatic magnetoacoustic wave modes supported by systems of prominence threads. Prominence fine-structures are modeled as parallel, homogeneous and infinite cylinders embedded in a coronal environment. The magnetic field is uniform and parallel to the axis of threads. Configurations of identical and nonidentical threads are both explored. We apply the T-matrix theory of acoustic scattering to obtain the oscillatory frequency and the eigenfunctions of linear magnetosonic disturbances. We find that the existence of wave modes with a collective dynamics, i.e. those that produce significant perturbations in all threads, is only possible when the Doppler-shifted individual frequencies of threads are very similar. This can be only achieved for very particular values of the plasma physical conditions and flow velocities within threads.

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

Publication Status: Submitted in ApJ
Last Modified: 2008-09-30 09:31
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Subject will be restored when possible  

Roberto Soler   Submitted: 2008-03-18 05:15

High-resolution observations show that oscillations and waves in prominence threads are common and that they are attenuated in a few periods. In addition, observers have also reported the presence of material flows in such prominence fine-structures. Here we investigate the time damping of non-leaky oscillations supported by a homogeneous cylindrical prominence thread embedded in an unbounded corona and with a steady mass flow. Thermal conduction and radiative losses are taken into account as damping mechanisms, and the effect of these non-ideal effects and the steady flow on the attenuation of oscillations is assessed. We solve the general dispersion relation for linear, non-adiabatic magnetoacoustic and thermal waves supported by the model, and find that slow and thermal modes are efficiently attenuated by non-adiabatic mechanisms. On the contrary, fast kink modes are much less affected and their damping times are much larger than those observed. The presence of flow has no effect on the damping of slow and thermal waves, whereas fast kink waves are more (less) attenuated when they propagate parallel (anti-parallel) to the flow direction. Although the presence of steady mass flows improves the efficiency of non-adiabatic mechanisms on the attenuation of transverse, kink oscillations for parallel propagation to the flow, its effect is still not enough to obtain damping times compatible with observations.

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

Publication Status: Submitted in ApJ
Last Modified: 2008-09-23 21:13
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Subject will be restored when possible  

Roberto Soler   Submitted: 2008-01-24 05:52

Context. Observations show that small-amplitude prominence oscillations are usually damped after a few periods. This phenomenon has been theoretically investigated in terms of non-ideal magnetoacoustic waves, non-adiabatic effects being the best candidates to explain the damping in the case of slow modes. Aims. We study the attenuation of non-adiabatic magnetoacoustic waves in a slab prominence embedded in the coronal medium. We assume an equilibrium configuration with a transverse magnetic field to the slab axis and investigate wave damping by thermal conduction and radiative losses. Methods. The magnetohydrodynamic equations are considered in their linearised form and terms representing thermal conduction, radiation and heating are included in the energy equation. The differential equations that govern linear slow and fast modes are numerically solved to obtain the complex oscillatory frequency and the corresponding eigenfunctions. Results. Coronal thermal conduction and radiative losses from the prominence plasma reveal as the most relevant damping mechanisms. Both mechanisms govern together the attenuation of hybrid modes, whereas prominence radiation is responsible for the damping of internal modes and coronal conduction essentially dominates the attenuation of external modes. In addition, the energy transfer between the prominence and the corona caused by thermal conduction has a noticeable effect on the wave stability, radiative losses from the prominence plasma being of paramount importance for the thermal stability of fast modes. Conclusions. Slow modes are efficiently damped, with damping times compatible with observations. On the contrary, fast modes are less attenuated by non-adiabatic effects and their damping times are several orders of magnitude larger than those observed. The presence of the corona causes a decrease of the damping times with respect to those of an isolated prominence slab, but its effect is still insufficient to obtain damping times of the order of the period in the case of fast modes.

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

Publication Status: Submitted to A&A
Last Modified: 2008-01-24 07:54
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Subject will be restored when possible  

Roberto Soler   Submitted: 2007-10-16 11:00

Oscillations of magnetic structures in the solar corona have often been interpreted in terms of magnetohydrodynamic waves. We study the adiabatic magnetoacoustic modes of a prominence plasma slab with a uniform longitudinal magnetic field, surrounded by a prominence-corona transition region (PCTR) and a coronal medium. Considering linear small-amplitude oscillations, the dispersion relation for the magnetoacoustic slow and fast modes is deduced assuming evanescent-like perturbations in the coronal medium. In the system without PCTR, a classification of the oscillatory modes according to the polarisation of their eigenfunctions is made in order to distinguish modes with fast-like or slow-like properties. Internal and external slow modes are governed by the prominence and coronal properties respectively, and fast modes are mostly dominated by prominence conditions for the observed wavelengths. In addition, the inclusion of an isothermal PCTR does not substantially influence the mode frequencies, but new solutions (PCTR slow modes) are present.

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

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2007-10-17 11:38
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The effect of the solar corona on the attenuation of small-amplitude prominence oscillations. I. Longitudinal magnetic field  

Roberto Soler   Submitted: 2007-04-13 04:43

Context. One of the typical features shown by observations of solar prominence oscillations is that they are damped in time and that the values of the damping times are usually between one and three times the corresponding oscillatory period. However, the mechanism responsible for the attenuation is still not well-known. Aims. Thermal conduction, optically thin or thick radiation and heating are taken into account in the energy equation, and their role on the attenuation of prominence oscillations is evaluated. Methods. The dispersion relation for linear non-adiabatic magnetoacoustic waves is derived considering an equilibrium made of a prominence plasma slab embedded in an unbounded corona. The magnetic field is orientated along the direction parallel to the slab axis and has the same strength in all regions. By solving the dispersion relation for a fixed wavenumber, a complex oscillatory frequency is obtained, and the period and the damping time are computed. Results. The effect of conduction and radiation losses is different for each magnetoacoustic mode and depends on the wavenumber. In the observed range of wavelengths the internal slow mode is attenuated by radiation from the prominence plasma, the fast mode by the combination of prominence radiation and coronal conduction and the external slow mode by coronal conduction. The consideration of the external corona is of paramount importance in the case of the fast and external slow modes, whereas it does not affect the internal slow modes at all. Conclusions. Non-adiabatic effects are efficient damping mechanisms for magnetoacoustic modes, and the values of the obtained damping times are compatible with those observed.

Authors: R. Soler, R. Oliver, J. L. Ballester
Projects:

Publication Status: Accepted for publication in A&A
Last Modified: 2007-06-27 09:23
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Abstracts by Author
Transverse waves in coronal flux tubes with thick boundaries: The effect of longitudinal flows
Energy transport and heating by torsional Alfv?n waves propagating from the photosphere to the corona in the quiet Sun
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

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

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