E-Print Archive

There are 3945 abstracts currently viewable.


Search:

Advanced Search
Options
Main Page Add New E-Print Submitter
Information
Feedback
News Help/FAQ About Preferences
Manage Key Phrase
Notification
Fast magnetohydrodynamic oscillation of longitudinally inhomogeneous prominence threads: an analogue with quantum harmonic oscillator  

Teimuraz Zaqarashvili   Submitted: 2014-04-11 02:46

Previous works indicate that the frequency ratio of second and first harmonics of kink oscillations tends towards 3 in the case of prominence threads. We aim to study the magnetohydrodynamic oscillations of longitudinally inhomogeneous prominence threads and to shed light on the problem of the frequency ratio. The classical Sturm-Liouville problem is used for the threads with longitudinally inhomogeneous plasma density. We show that the spatial variation of total pressure perturbations along the thread is governed by the stationary Schr?dinger equation, where the longitudinal inhomogeneity of plasma density stands for the potential energy. The Schr?dinger equation appears as the equation of quantum harmonic oscillator for a parabolic profile of plasma density. Consequently, the equation has bounded solutions in terms of Hermite polynomials. Boundary conditions at the thread surface lead to a transcendental dispersion equation with Bessel functions. The thin flux tube approximation of the dispersion equation shows that the frequency of kink waves is proportional to the expression α 2n+1), where α is the density inhomogeneity parameter, and n the longitudinal mode number. Consequently, the ratio of the frequencies of second and first harmonics tends to 3 in prominence threads. The numerical solution of the dispersion equation shows that the ratio decreases only slightly for thicker tubes in the case of less longitudinal inhomogeneity of the external density, therefore the thin flux tube limit is a good approximation for prominence oscillations. However, stronger longitudinal inhomogeneity of external density may lead to the significant shift in the frequency ratio for wider tubes, and therefore the thin tube approximation may fail. The tendency of frequency ratio of second and first harmonics towards 3 in prominence threads is explained by the analogy of the oscillations with quantum harmonic oscillator, where the density inhomogeneity of the threads plays a role as the potential energy.

Authors: Lomineishvili, S.N., Zaqarashvili, T.V., Zhelyazkov, I. and Tevzadze, A.G.
Projects: None

Publication Status: Accepted in A&A
Last Modified: 2014-04-14 12:51
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Twisted magnetic flux tubes in the solar wind  

Teimuraz Zaqarashvili   Submitted: 2014-02-11 08:51

Magnetic flux tubes in the solar wind can be twisted as they are transported from the solar surface, where the tubes are twisted owing to photospheric motions. It is suggested that the twisted magnetic tubes can be detected as the variation of total (thermal+magnetic) pressure during their passage through observing satellite. We show that the total pressure of several observed twisted tubes resembles the theoretically expected profile. The twist of isolated magnetic tube may explain the observed abrupt changes of magnetic field direction at tube walls. We have also found some evidence that the flux tube walls can be associated with local heating of the plasma and elevated proton and electron temperatures. For the tubes aligned with the Parker spiral, the twist angle can be estimated from the change of magnetic field direction. Stability analysis of twisted tubes shows that the critical twist angle of the tube with a homogeneous twist is 700, but the angle can further decrease owing to the motion of the tube with regards to the solar wind stream. The tubes with a stronger twist are unstable to the kink instability, therefore they probably can not reach 1 AU.

Authors: Zaqarashvili, T.V., V"or"os, Z., Narita, Y., Bruno, R.
Projects: Wind

Publication Status: ApJL (in press)
Last Modified: 2014-02-11 12:20
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Rossby waves and polar spots in rapidly rotating stars: Implications for stellar wind evolution  

Teimuraz Zaqarashvili   Submitted: 2013-11-20 07:41

Rapidly rotating stars show short-period oscillations in magnetic activity and polar appearance of starspots. The aim of this paper is to study large-scale shallow water waves in the tachoclines of rapidly rotating stars and their connection to the periodicity and the formation of starspots at high latitudes. Shallow-water magnetohydrodynamic equations were used to study the dynamics of large-scale waves at the rapidly rotating stellar tachoclines in the presence of toroidal magnetic field. Dispersion relations and latitudinal distribution of wave modes were derived. We found that low-frequency magnetic Rossby waves tend to be located at poles, but high-frequency magnetic Poincar'e waves are concentrated near the equator in rapidly rotating stars. These results have important implications for the evolution of the stellar wind in young Sun-like stars. Unstable magnetic Rossby waves may lead to the local enhancement of magnetic flux at high latitudes of tachoclines in rapidly rotating stars. The enhanced magnetic flux may rise upwards owing to the magnetic buoyancy in the form of tubes and appear as starspots at polar regions. Magnetic Rossby waves may also cause observed short-term periodicity in the stellar magnetic activity.

Authors: Zaqarashvili, T.V., Oliver, R., Ballester, J.L., Carbonell, M., Khodachenko, M.L., Lammer, H., Leitzinger, M. and Odert, P.
Projects: None

Publication Status: Published in A&A
Last Modified: 2013-11-20 07:48
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Kelvin-Helmholtz instability of twisted magnetic flux tubes in the solar wind  

Teimuraz Zaqarashvili   Submitted: 2013-11-20 07:29

Solar wind plasma is supposed to be structured in magnetic flux tubes carried from the solar surface. Tangential velocity discontinuity near the boundaries of individual tubes may result in Kelvin-Helmholtz instability, which may contribute into the solar wind turbulence. While the axial magnetic field may stabilize the instability, a small twist in the magnetic field may allow to sub-Alfvénic motions to be unstable. We aim to study the Kelvin-Helmholtz instability of twisted magnetic flux tube in the solar wind with different configurations of external magnetic field. We use magnetohydrodynamic equations in the cylindrical geometry and derive the dispersion equations governing the dynamics of twisted magnetic flux tube moving along its axis in the cases of untwisted and twisted external fields. Then we solve the dispersion equations analytically and numerically and found thresholds for Kelvin-Helmholtz instability in both cases of external field. Both analytical and numerical solutions show that the Kelvin-Helmholtz instability is suppressed in the twisted tube by external axial magnetic field for sub-Alfvénic motions. However, even small twist in the external magnetic field allows the Kelvin-Helmholtz instability to be developed for any sub-Alfvénic motions. The unstable harmonics correspond to vortices with high azimuthal mode numbers, which are carried by the flow. Twisted magnetic flux tubes can be unstable to Kelvin-Helmholtz instability when they move with small speed relative to main solar wind stream, then the Kelvin-Helmholtz vortices may significantly contribute into the solar wind turbulence.

Authors: Zaqarashvili, T.V., V"or"os, Z. and Zhelyazkov, I.
Projects: None

Publication Status: Accepted in A&A
Last Modified: 2013-11-20 07:48
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Radio seismology of the outer solar corona  

Teimuraz Zaqarashvili   Submitted: 2013-11-20 07:25

Observed oscillations of coronal loops in extreme ultraviolet (EUV) lines have been successfully used to estimate plasma parameters in the inner corona (< 0.2 R, where R is the solar radius). However, coronal seismology in EUV lines fails for higher altitudes because of rapid decrease in line intensity. We aim to use radio observations to estimate the plasma parameters of the outer solar corona (> 0.2 R). We used the large Ukrainian radio telescope URAN-2 to observe type IV radio bursts at the frequency range of 8-32 MHz during the time interval of 09:50-12:30 UT on April 14, 2011. The burst was connected to C2.3 flare, which occurred in AR 11190 during 09:38-09:49 UT. The dynamic spectrum of radio emission shows clear quasi-periodic variations in the emission intensity at almost all frequencies. Wavelet analysis at four different frequencies (29 MHz, 25 MHz, 22 MHz, and 14 MHz) shows the quasi-periodic variation of emission intensity with periods of 34 min and 23 min. The periodic variations can be explained by the first and second harmonics of vertical kink oscillation of transequatorial coronal loops, which were excited by the same flare. The apex of transequatorial loops may reach up to 1.2 R altitude. We derive and solve the dispersion relation of trapped magnetohydrodynamic (MHD) oscillations in a longitudinally inhomogeneous magnetic slab. The analysis shows that a thin (with width to length ratio of 0.1), dense (with the ratio of internal and external densities of > 20) magnetic slab with weak longitudinal inhomogeneity may trap the observed oscillations. Seismologically estimated Alfvén speed inside the loop at the height of 1 R is 1000 km s/s. The magnetic field strength at this height is estimated as 0.9 G. Extrapolation of magnetic field strength to the inner corona gives 10 G at the height of 0.1 R. Radio observations can be successfully used for the sounding of the outer solar corona, where EUV observations of coronal loops fail. Therefore, radio seismology of the outer solar corona is complementary to EUV seismology of the inner corona.

Authors: Zaqarashvili, T.V., Melnik, V.N., Brazhenko, A.I., Panchenko, M., Konovalenko, A.A., Franzuzenko, A.V., Dorovskyy, V.V., Rucker, H.O.
Projects: None

Publication Status: Published in A&A
Last Modified: 2013-11-20 07:48
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Torsional Alfvén waves in partially ionized solar plasma: effects of neutral helium and stratification  

Teimuraz Zaqarashvili   Submitted: 2013-11-20 07:19

Ion-neutral collisions may lead to the damping of Alfvén waves in chromospheric and prominence plasmas. Neutral helium atoms enhance the damping in certain temperature intervals, where the ratio of neutral helium and neutral hydrogen atoms is increased. Therefore, the height dependence of the ionization degrees of hydrogen and helium may influence the damping rate of Alfvén waves. We aim to study the effect of neutral helium on the damping of Alfvén waves in stratified, partially ionized plasma of the solar chromosphere. We consider a magnetic flux tube, which is expanded up to 1000 km height and then becomes vertical owing to merging with neighboring tubes, and study the dynamics of linear torsional Alfvén waves in the presence of neutral hydrogen and neutral helium atoms. We start with a three-fluid description of plasma and subsequently derive single-fluid magnetohydrodynamic (MHD) equations for torsional Alfvén waves. Thin flux tube approximation allows us to obtain the dispersion relation of the waves in the lower part of tubes, while the spatial dependence of steady-state Alfvén waves is governed by a Bessel-type equation in the upper parts of the tubes. Consecutive derivation of single-fluid MHD equations results in a new Cowling diffusion coefficient in the presence of neutral helium, which is different from the previously used one. We find that shorter period (< 5 s) torsional Alfvén waves damp quickly in the chromospheric network owing to ion-neutral collision. On the other hand, longer period (> 5 s) waves do not reach the transition region because they become evanescent at lower heights in the network cores. Propagation of torsional Alfvén waves through the chromosphere into the solar corona should be considered with caution: low-frequency waves are evanescent owing to the stratification, while high-frequency waves are damped by ion-neutral collisions.

Authors: Zaqarashvili, T.V., Khodachenko, M.L. and Soler, R.
Projects: None

Publication Status: published in A&A
Last Modified: 2013-11-20 07:48
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Cut-off wavenumber of Alfvén waves in partially ionized plasmas of the solar atmosphere  

Teimuraz Zaqarashvili   Submitted: 2013-11-20 07:14

Alfvén wave dynamics in partially ionized plasmas of the solar atmosphere shows that there is indeed a cut-off wavenumber, i.e. the Alfvén waves with wavenumbers higher than the cut-off value are evanescent. The cut-off wavenumber appears in single-fluid magnetohydrodynamic (MHD) approximation but it is absent in a multi-fluid approach. Up to now, an explanation for the existence of the cut-off wavenumber is still missing. The aim of this paper is to point out the reason for the appearance of a cut-off wavenumber in single-fluid MHD. Beginning with three-fluid equations (with electrons, protons and neutral hydrogen atoms), we performed consecutive approximations until we obtained the usual single-fluid description. We solved the dispersion relation of linear Alfvén waves at each step and sought the approximation responsible of the cut-off wavenumber appearance. We have found that neglecting inertial terms significantly reduces the real part of the Alfvén frequency although it never becomes zero. Therefore, the cut-off wavenumber does not exist at this stage. However, when the inertial terms together with the Hall term in the induction equation are neglected, the real part of the Alfvén frequency becomes zero. The appearance of a cut-off wavenumber, when Alfvén waves in partially ionized regions of the solar atmosphere are studied, is the result of neglecting inertial and Hall terms, therefore it has no physical origin.

Authors: Zaqarashvili, T. V., Carbonell, M., Ballester J. L. and Khodachenko, M. L.
Projects: None

Publication Status: published in A&A
Last Modified: 2013-11-20 07:48
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Damping of Alfvén waves in solar partially ionized plasmas: effect of neutral helium in multi-fluid approach  

Teimuraz Zaqarashvili   Submitted: 2011-09-07 04:18

Chromospheric and prominence plasmas contain neutral atoms, which may change the plasma dynamics through collision with ions. Most of the atoms are neutral hydrogen, but a significant amount of neutral helium may also be present in the plasma with a particular temperature. Damping of MHD waves due to ion collision with neutral hydrogen is well studied, but the effects of neutral helium are largely unknown. We aim to study the effect of neutral helium in the damping of Alfvén waves in solar partially ionized plasmas. We consider three-fluid magnetohydrodynamic (MHD) approximation, where one component is electron-proton-singly ionized helium and other two components are the neutral hydrogen and neutral helium atoms. We derive the dispersion relation of linear Alfvén waves in isothermal and homogeneous plasma. Then we solve the dispersion relation and derive the damping rates of Alfvén waves for different plasma parameters. The presence of neutral helium significantly enhances the damping of Alfvén waves compared to the damping due to neutral hydrogen at certain values of plasma temperature (10000-40000 K) and ionization. Damping rates have a peak near the ion-neutral collision frequency, but decrease for the higher part of wave spectrum. Collision of ions with neutral helium atoms can be of importance for the damping of Alfvén waves in chromospheric spicules and in prominence-corona transition regions.

Authors: Zaqarashvili, T.V., Khodachenko, M.L., and Rucker, H.O.
Projects: None

Publication Status: Accepted in A&A
Last Modified: 2011-09-07 05:43
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Magnetohydrodynamic waves in solar partially ionized plasmas: two-fluid approach  

Teimuraz Zaqarashvili   Submitted: 2011-01-21 02:17

Partially ionized plasma is usually described by single-fluid approach, where the ion-neutral collision effects are expressed by Cowling conductivity in the induction equation. However, the single-fluid approach is not valid for the time-scales less than ion-neutral collision time. For these time-scales the two-fluid description is better approximation. We derive the dynamics of magnetohydrodynamic waves in two-fluid partially ionized plasmas and to compare the results with those obtained under single-fluid description. Two-fluid magnetohydrodynamic equations are used, where ion-electron plasma and neutral particles are considered as separate fluids. Dispersion relations of linear magnetohydrodynamic waves are derived for simplest case of homogeneous medium. Frequencies and damping rates of waves are obtained for different parameters of background plasma. We found that two- and single-fluid descriptions give similar results for low frequency waves. However, the dynamics of MHD waves in two-fluid approach is significantly changed when the wave frequency becomes comparable or higher than ion-neutral collision frequency. Alfvén and fast magneto-acoustic waves attain their maximum damping rate at particular frequencies (for example, the peak frequency equals 2.5 ion-neutral collision frequency for 50 % of neutral Hydrogen) in wave spectrum. The damping rates are reduced for higher frequency waves. The new mode of slow magneto-acoustic wave appears for higher frequency branch, which is connected to neutral hydrogen fluid. The single-fluid approach perfectly deals with slow processes in partially ionized plasmas, but fails for time-scales smaller than ion-neutral collision time. Therefore, two-fluid approximation should be used for the description of relatively fast processes. Some results of single-fluid description, for example the damping of high-frequency Alfvén waves in the solar chromosphere due to ion-neutral collisions, should be revised in future.

Authors: Zaqarashvili, T. V., Khodachenko, M. K., Rucker, H. O.
Projects: None

Publication Status: A&A (accepted)
Last Modified: 2011-01-21 08:46
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

The excitation of 5-min oscillations in the solar corona  

Teimuraz Zaqarashvili   Submitted: 2011-01-21 02:13

We aim to study excitation of the observed 5-min oscillations in the solar corona by localized pulses that are launched in the photosphere. We solve the full set of nonlinear one-dimensional Euler equations numerically for the velocity pulse propagating in the solar atmosphere that is determined by the realistic temperature profile. Numerical simulations show that an initial velocity pulse quickly steepens into a leading shock, while the nonlinear wake in the chromosphere leads to the formation of consecutive pulses. The time interval between arrivals of two neighboring pulses to a detection point in the corona is approximately 5 min. Therefore, the consecutive pulses may result in the 5-min oscillations that are observed in the solar corona. The 5-min oscillations observed in the solar corona can be explained in terms of consecutive shocks that result from impulsive triggers launched within the solar photosphere by granulation and/or reconnection.

Authors: Zaqarashvili, T. V., Murawski, K., Khodachenko, M. K., Lee, D.
Projects: None

Publication Status: A&A (accepted)
Last Modified: 2011-01-21 08:46
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Quasi-biennial oscillations in the solar tachocline caused by magnetic Rossby wave instabilities  

Teimuraz Zaqarashvili   Submitted: 2010-11-08 01:48

Quasi-biennial oscillations (QBO) are frequently observed in the solar activity indices. However, no clear physical mechanism for the observed variations has been suggested so far. Here we study the stability of magnetic Rossby waves in the solar tachocline using the shallow water magnetohydrodynamic approximation. Our analysis shows that the combination of typical differential rotation and a toroidal magnetic field with a strength > 105 G triggers the instability of the m=1 magnetic Rossby wave harmonic with a period of 2 years. This harmonic is antisymmetric with respect to the equator and its period (and growth rate) depends on the differential rotation parameters and the magnetic field strength. The oscillations may cause a periodic magnetic flux emergence at the solar surface and consequently may lead to the observed QBO in the solar activity features. The period of QBO may change throughout the cycle, and from cycle to cycle, due to variations of the mean magnetic field and differential rotation in the tachocline.

Authors: Zaqarashvili, T.V., Carbonell, M., Oliver, R. and Ballester, J.L.
Projects: None

Publication Status: ApJ (in press)
Last Modified: 2010-11-08 07:34
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Propagation of a sausage soliton in the solar lower atmosphere observed by Hinode/SOT  

Teimuraz Zaqarashvili   Submitted: 2010-04-19 08:18

Acoustic waves and pulses propagating from the solar photosphere upwards may quickly develop into shocks due to the rapid decrease of atmospheric density. However, if they propagate along a magnetic flux tube, then the non-linear steepening may be balanced by tube dispersion effects. This may result in the formation of a sausage soliton. The aim of this Letter is to report observational evidence of a sausage soliton in the solar chromosphere. A time series of the CaII H line obtained at the solar limb with the Solar Optical Telescope (SOT) on board Hinode is analysed. Observations show an intensity blob, which propagates from 500 to 1700 km above the solar surface with a mean apparent speed of 35 km s-1. The speed is much higher than the expected local sound speed, therefore the blob cannot be a simple pressure pulse. The blob speed, length-to-width ratio and relative intensity correspond to a slow sausage soliton propagating along a magnetic tube. The blob width increases with height corresponding to the magnetic tube expansion in the stratified atmosphere. Propagation of the intensity blob may be the first observational evidence of a slow sausage soliton in the solar atmosphere.

Authors: Zaqarashvili, T. V., Kukhianidze, V. and Khodachenko, M. L.
Projects: Hinode/SOT

Publication Status: MNRAS (in press)
Last Modified: 2010-04-19 08:23
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Magnetic Rossby waves in the solar tachocline and Rieger-type periodicities  

Teimuraz Zaqarashvili   Submitted: 2009-11-25 07:29

Apart from the 11-year solar cycle, another periodicity around 155-160 days was discovered during solar cycle 21 in high energy solar flares, and its presence in sunspot areas and strong magnetic flux has been also reported. This periodicity has an elusive and enigmatic character, since it usually appears only near the maxima of solar cycles, and seems to be related with a periodic emergence of strong magnetic flux at the solar surface. Therefore, it is probably connected with the tachocline, a thin layer located near the base of the solar convection zone, where strong dynamo magnetic field is stored. We study the dynamics of Rossby waves in the tachocline in the presence of a toroidal magnetic field and latitudinal differential rotation. Our analysis shows that the magnetic Rossby waves are generally unstable and that the growth rates are sensitive to the magnetic field strength and to the latitudinal differential rotation parameters. Variation of the differential rotation and the magnetic field strength throughout the solar cycle enhance the growth rate of a particular harmonic in the upper part of the tachocline around the maximum of the solar cycle. This harmonic is symmetric with respect to the equator and has a period of 155-160 days. A rapid increase of the wave amplitude could give place to a magnetic flux emergence leading to observed periodicities in solar activity indicators related with magnetic flux.

Authors: Zaqarashvili, T.V. , Carbonell, M., Oliver, R. and Ballester, J.L.
Projects: None

Publication Status: Accepted in ApJ
Last Modified: 2009-11-25 10:56
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Acoustic oscillations in the field-free, gravitationally stratified cavities under solar bipolar magnetic canopies  

Teimuraz Zaqarashvili   Submitted: 2009-06-10 05:48

The main goal is to study the dynamics of the gravitationally stratified, field-free cavities in the solar atmosphere, located under small-scale, cylindrical magnetic canopies, in response to explosive events in the lower-lying regions (due to granulation, small-scale magnetic reconnection, etc.). We derive the two-dimensional Klein-Gordon equation for isothermal density perturbations in cylindrical coordinates. The equation is first solved by a standard normal mode analysis in order to obtain the free oscillation spectrum of the cavity. Then, the equation is solved in the case of impulsive forcing associated to a pressure pulse specified in the lower-lying regions. The normal mode analysis shows that the entire cylindrical cavity of granular dimensions tends to oscillate with frequencies of 5-8 mHz and also with the atmospheric cut-off frequency. Furthermore, the passage of a pressure pulse, excited in the convection zone, sets up a wake in the cavity oscillating with the same cut-off frequency. The wake oscillations can resonate with the free oscillation modes, which leads to an enhanced observed oscillation power. The resonant oscillations of these cavities explain the observed power halos near magnetic network cores and active regions.

Authors: Kuridze, D., Zaqarashvili, T.V., Shergelashvili, B.M. and Poedts, S.
Projects: None

Publication Status: A&A (accepted)
Last Modified: 2009-06-10 09:18
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Oscillations and waves in solar spicules  

Teimuraz Zaqarashvili   Submitted: 2009-06-10 05:38

Since their discovery, spicules have attracted increased attention as energy/mass bridges between the dense and dynamic photosphere and the tenuous hot solar corona. Mechanical energy of photospheric random and coherent motions can be guided by magnetic field lines, spanning from the interior to the upper parts of the solar atmosphere, in the form of waves and oscillations. Since spicules are one of the most pronounced features of the chromosphere, the energy transport they participate in can be traced by the observations of their oscillatory motions. Oscillations in spicules have been observed for a long time. However the recent high-resolutions and high cadence space and ground based facilities with superb spatial, temporal and spectral capacities brought new aspects in the research of spicule dynamics. Here we review the progress made in imaging and spectroscopic observations of waves and oscillations in spicules. The observations are accompanied by a discussion on theoretical modelling and interpretations of these oscillations. Finally, we embark on the recent developments made on the presence and role of Alfvén and kink waves in spicules. We also address the extensive debate made on the Alfvén versus kink waves in the context of the explanation of the observed transverse oscillations of spicule axes.

Authors: Zaqarashvili, T.V. and Erdelyi, R.
Projects: Hinode/SOT

Publication Status: Space Science Reviews (accepted)
Last Modified: 2009-06-10 09:18
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Helical motion of magnetic flux tubes in the solar atmosphere  

Teimuraz Zaqarashvili   Submitted: 2008-07-04 02:29

Photospheric granulation may excite transverse kink pulses in anchored vertical magnetic flux tubes. The pulses propagate upwards along the tubes with the kink speed, while oscillating wakes are formed behind the wave front in a stratified atmosphere. The wakes oscillate at the kink cut-off frequency of stratified medium and gradually decay in time. When two or more consecutive kink pulses with different polarizations propagate in the same thin tube, then the wakes corresponding to different pulses may superimpose. The superposition sets up helical motions of magnetic flux tubes in the photosphere/chromosphere as seen by recent Hinode movies. The energy carried by the pulses is enough to heat the solar chrmosphere/corona and accelerate the solar wind.

Authors: Zaqarashvili, T.V. and Skhirtladze, N.
Projects: Hinode/SOT

Publication Status: ApJL (accepted)
Last Modified: 2008-09-23 20:57
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Subject will be restored when possible  

Teimuraz Zaqarashvili   Submitted: 2008-02-22 00:48

Observations show the increase of high-frequency wave power near magnetic network cores and active regions in the solar lower atmosphere. This phenomenon can be explained by the interaction of acoustic waves with a magnetic field. We consider small-scale, bipolar, magnetic field canopy structure near the network cores and active regions overlying field-free cylindrical cavities of the photosphere. Solving the plasma equations we get the analytical dispersion relation of acoustic oscillations in the field-free cavity area. We found that the m = 1 mode, where m is azimuthal wave number, cannot be trapped under the canopy due to energy leakage upwards. However, higher (m > 1) harmonics can be easily trapped leading to the observed acoustic power halos under the canopy.

Authors: D. Kuridze, T. V. Zaqarashvili, B. M. Shergelashvili1, S. Poedts
Projects: Hinode/SOT

Publication Status: Accepted in Annales Geophysicae
Last Modified: 2008-09-23 21:25
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Doppler shift oscillations in solar spicules  

Teimuraz Zaqarashvili   Submitted: 2007-08-16 03:16

Consecutive height series of Ha spectra in solar limb spicules taken on the 53 cm coronagraph of Abastumani Astrophysical Observatory at the heights of 3800-8700 km above the photosphere have been analyzed. The aim is to observe oscillatory phenomena in spicules and consequently to trace wave propagations through the chromosphere. The Discrete Fourier Transform analysis of Ha Doppler shift time series constructed from the observed spectra at each height is used. Doppler velocities of solar limb spicules show oscillations with periods of 20-55 and 75-110 s. There is also the clear evidence of 3-min oscillations at the observed heights. The oscillations can be caused by wave propagations in thin magnetic flux tubes anchored in the photosphere. We suggest the granulation as a possible source for the wave excitation. Observed waves can be used as a tool for spicule seismology; the magnetic field strength in spicules at the height of about 6000 km above the photosphere is estimated as 12-15 G.

Authors: Zaqarashvili, T.V., Khutsishvili, E., Kukhianidze, V. and Ramishvili, G.
Projects: None

Publication Status: A&A (accepted)
Last Modified: 2007-08-16 08:37
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Torsional oscillations of longitudinally inhomogeneous coronal loops  

Teimuraz Zaqarashvili   Submitted: 2007-04-03 04:08

We explore the effect of an inhomogeneous mass density field on frequencies and wave profiles of torsional Alfvén oscillations in solar coronal loops. Dispersion relations for torsional oscillations are derived analytically in limits of weak and strong inhomogeneities. These analytical results are verified by numerical solutions, which are valid for a wide range of inhomogeneity strength. It is shown that the inhomogeneous mass density field leads to the reduction of a wave frequency of torsional oscillations, in comparison to that of estimated from massdensity at the loop apex. This frequency reduction results from the decrease of an average Alfvén speed as far as the inhomogeneous loop is denser at its footpoints. The derived dispersion relations and wave profiles are important for potential observations of torsional oscillations which result in periodic variations of spectral line widths.Torsional oscillations offer an additional powerful tool for a development of coronal seismology.

Authors: T.V. Zaqarashvili and K. Murawski
Projects:

Publication Status: A&A (accepted)
Last Modified: 2007-04-05 09:39
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

Resonant energy conversion of 3-minute intensity oscillations into Alfvén waves in the solar atmosphere  

Teimuraz Zaqarashvili   Submitted: 2007-03-19 04:02

Nonlinear coupling between 3-minute oscillations and Alfvén waves in the solar lower atmosphere is studied. 3-minute oscillations are considered as acoustic waves trapped in a chromospheric cavity and oscillating along transversally inhomogeneous vertical magnetic field. It is shown that under the action of the oscillations the temporal dynamics of Alfvén waves is governed by Mathieu equation. Consequently, the harmonics of Alfvén waves with twice period and wavelength of 3-minute oscillations grow exponentially in time near the layer where the sound and Alfvén speeds equal. Thus the 3-minute oscillations are resonantly absorbed by pure Alfvén waves near this resonant layer. The resonant Alfvén waves may penetrate into the solar corona taking energy from the chromosphere. Therefore the layer c_s=vA may play a role of energy channel for otherwise trapped acoustic oscillations.

Authors: Kuridze, D. and Zaqarashvili, T.V.
Projects:

Publication Status: accepted in Journal of Atmospheric and Solar-Terrestrial Physics
Last Modified: 2007-04-05 09:24
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 


[Older Entries]
Key
Go to main E-Print pageGo to main E-Print page.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
Delete AbstractDelete abstract.

Abstracts by Author
Fast magnetohydrodynamic oscillation of longitudinally inhomogeneous prominence threads: an analogue with quantum harmonic oscillator
Twisted magnetic flux tubes in the solar wind
Rossby waves and polar spots in rapidly rotating stars: Implications for stellar wind evolution
Kelvin-Helmholtz instability of twisted magnetic flux tubes in the solar wind
Radio seismology of the outer solar corona
Torsional Alfven waves in partially ionized solar plasma: effects of neutral helium and stratification
Cut-off wavenumber of Alfven waves in partially ionized plasmas of the solar atmosphere
Damping of Alfven waves in solar partially ionized plasmas: effect of neutral helium in multi-fluid approach
Magnetohydrodynamic waves in solar partially ionized plasmas: two-fluid approach
The excitation of 5-min oscillations in the solar corona
Quasi-biennial oscillations in the solar tachocline caused by magnetic Rossby wave instabilities
Propagation of a sausage soliton in the solar lower atmosphere observed by Hinode/SOT
Magnetic Rossby waves in the solar tachocline and Rieger-type periodicities
Acoustic oscillations in the field-free, gravitationally stratified cavities under solar bipolar magnetic canopies
Oscillations and waves in solar spicules
Helical motion of magnetic flux tubes in the solar atmosphere
Subject will be restored when possible
Doppler shift oscillations in solar spicules
Torsional oscillations of longitudinally inhomogeneous coronal loops
Resonant energy conversion of 3-minute intensity oscillations into Alfven waves in the solar atmosphere
Coupling between radial and torsional oscillations in a magnetized plasma and possible stellar applications

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

Archive Maintainer
Alisdair Davey



© 2003 Solar Physics Group - Montana State University