scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Wave propagation in a magnetic cylinder

01 Oct 1983-Solar Physics (Kluwer Academic Publishers)-Vol. 88, Iss: 1, pp 179-191
TL;DR: In this article, the authors investigated the nature of oscillations in a magnetic cylinder embedded in magnetic environment and showed that the standard slender flux tube analysis of a kink mode in a cylinder excludes the possibility of a second mode, which arises under photospheric conditions.
Abstract: The nature of oscillations in a magnetic cylinder embedded in a magnetic environment is investigated. It is shown that the standard slender flux tube analysis of a kink mode in a cylinder excludes the possibility of a second mode, which arises under photospheric conditions. Under coronal conditions, two widely separated classes of oscillation can be freely sustained, one on an acoustic time-scale and the other on an Alfvenic time-scale. The acoustic-type oscillations are always present, but the much shorter period, Alfvenic-type, oscillations arise only in high density (strictly, low Alfven velocity) loops. An application to waves in fibrils is also given, and suggests (following Wentzel, 1979) that they are fast kink waves propagating in a density enhancement.
Citations
More filters
Journal ArticleDOI
06 Aug 1999-Science
TL;DR: The imaging telescope on board the Transition Region and Coronal Explorer spacecraft observed the decaying transversal oscillations of a long and thin coronal loop in the 171 angstrom Fe(IX) emission line, finding the coronal dissipation coefficient to be eight to nine orders of magnitude larger than the theoretically predicted classical value.
Abstract: The imaging telescope on board the Transition Region and Coronal Explorer (TRACE) spacecraft observed the decaying transversal oscillations of a long [(130 +/- 6) x 10(exp 6) meters], thin [diameter (2.0 +/- 0.36) x 10(exp 6) meters], bright coronal loop in the 171 angstrom Fe-IX emission line. The oscillations were excited by a solar flare in the adjacent active region. The decay time of the oscillations is 12.1 +/- 6.7 minutes for an oscillation with a frequency 3.90 +/- 0.13 millihertz The coronal dissipation coefficient is estimated to be eight to nine orders of magnitude larger than the theoretically predicted classical value. The larger dissipation coefficient may solve existing difficulties with wave heating and reconnection theories.

945 citations

Journal ArticleDOI
TL;DR: In this article, spatial oscillations of coronal loops were detected in extreme-ultraviolet wavelengths (171 with the T ransition Region and Coronal Explorer, in the tem- Ae ) perature range of MK.
Abstract: We report here, for the —rst time, on spatial oscillations of coronal loops, which were detected in extreme-ultraviolet wavelengths (171 with the T ransition Region and Coronal Explorer, in the tem- Ae ) perature range of MK. The observed loop oscillations occurred during a —are that began at T e B 1.0¨1.5 1998 July 14, 12:55 UT and are most prominent during the —rst 20 minutes. The oscillating loops connect the penumbra of the leading sunspot to the —are site in the trailing portion. We identi—ed —ve oscillating loops with an average length of L \ 130,000 ^ 30,000 km. The transverse amplitude of the oscillations is A \ 4100 ^ 1300 km, and the mean period is T \ 280 ^ 30 s. The oscillation mode appears to be a standing wave mode (with —xed nodes at the footpoints). We investigate diUerent MHD wave modes and —nd that the fast kink mode with a period q \ 205(L /1010 cm~3)1@2 cm)(n e /109 (B/10 G)~1 s provides the best agreement with the observed period. We propose that the onset of loop oscillations in distant locations is triggered by a signal or disturbance that propagates from the central —are site with a radial speed of B700 km s~1. Because the observed loop oscillation periods are compa- rable to photospheric 5 minute oscillations, a resonant coupling between the two systems is possible. We further —nd evidence for global extreme-UV dimming in the entire active region possibly associated with a coronal mass ejection. Subject headings: Sun: coronaSun: —aresSun: oscillationsSun: UV radiation

927 citations

Journal ArticleDOI
TL;DR: In this paper, the authors show that a coronal flux tube with inhomogeneities on a small scale (confined to within a thin layer of order a�=! k in thickness) is able to support coherent oscillations for any length of time and so be observable.
Abstract: Motivated by recent Transition Region and Coronal Explorer (TRACE) observations of damped oscilla- tions in coronal loops, we consider analytically the motion of an inhomogeneous coronal magnetic tube of radius a in a zero-� plasma. An initially perturbed tube may vibrate in its kink mode of oscillation, but those vibrations are damped. The damping is due to resonant absorption, acting in the inhomogeneous regions of the tube, which leads to a transfer of energy from the kink mode to Alfven (azimuthal) oscillations within the inhomogeneous layer. We determine explicitly the decrement � (decay time � � 1 ) for a coronal flux tube whose plasma density varies only in a thin layer of thickness  on the tube boundary. The effect of viscosity is also considered. We show that, in general, the problem involves two distinct timescales, � � 1 and ! � 1 k R 1=3 , where R is the Reynolds number and !k is the frequency of the kink mode. Under coronal conditions (when � � 1 5 ! � 1 k R 1=3 ), the characteristic damping time of global oscillations is � � 1 . During this time, most of the energy in the initial perturbation is transferred into a resonant absorption layer of thickness of order  2 =a, with motions in this layer having an amplitude of order a= times the initial amplitude. We apply our results to the observations, suggesting that loop oscillations decay principally because of inhomogeneities in the loop. Our theory suggests that only those loops with density inhomogeneities on a small scale (confined to within a thin layer of order a�=! k in thickness) are able to support coherent oscillations for any length of time and so be observable. Loops with a more gradual density variation, on the scale of the tube radius a, do not exhibit pronounced oscillations. Subject headings: MHD — plasmas — Sun: corona — waves

513 citations


Cites background from "Wave propagation in a magnetic cyli..."

  • ...The theory of coronal loop oscillations has been developed in some detail for the special case of a straight cylinder of magnetic field embedded in magnetized plasma surroundings (see, e.g., Edwin & Roberts 1983)....

    [...]

  • ...2A e þ i 1=2 : ð47Þ The quantity !k is the frequency of kink oscillations of a thin homogeneous magnetic tube and has been discussed in Edwin & Roberts (1983) and Roberts (2000)....

    [...]

Journal ArticleDOI
20 Mar 2009-Science
TL;DR: The detection of oscillatory phenomena associated with a large bright-point group that is 430,000 square kilometers in area and located near the solar disk center suggests that these torsional Alfvén oscillations are induced globally throughout the entire brightening.
Abstract: The flow of energy through the solar atmosphere and the heating of the Sun's outer regions are still not understood. Here, we report the detection of oscillatory phenomena associated with a large bright-point group that is 430,000 square kilometers in area and located near the solar disk center. Wavelet analysis reveals full-width half-maximum oscillations with periodicities ranging from 126 to 700 seconds originating above the bright point and significance levels exceeding 99%. These oscillations, 2.6 kilometers per second in amplitude, are coupled with chromospheric line-of-sight Doppler velocities with an average blue shift of 23 kilometers per second. A lack of cospatial intensity oscillations and transversal displacements rules out the presence of magneto-acoustic wave modes. The oscillations are a signature of Alfven waves produced by a torsional twist of ±22 degrees. A phase shift of 180 degrees across the diameter of the bright point suggests that these torsional Alfven oscillations are induced globally throughout the entire brightening. The energy flux associated with this wave mode is sufficient to heat the solar corona.

462 citations

Journal ArticleDOI
TL;DR: In this paper, a review reflects the current trends in the observational study of coronal waves and oscillations (standing kink, sausage and longitudinal modes, propagating slow waves and fast wave trains, the search for torsional waves), theoretical modelling of interaction of magnetohydrodynamic (MHD) waves with plasma structures, and implementation of the theoretical results for the mode identification.
Abstract: Wave and oscillatory activity of the solar corona is confidently observed with modern imaging and spectral instruments in the visible light, EUV, X-ray and radio bands, and interpreted in terms of magnetohydrodynamic (MHD) wave theory. The review reflects the current trends in the observational study of coronal waves and oscillations (standing kink, sausage and longitudinal modes, propagating slow waves and fast wave trains, the search for torsional waves), theoretical modelling of interaction of MHD waves with plasma structures, and implementation of the theoretical results for the mode identification. Also the use of MHD waves for remote diagnostics of coronal plasma - MHD coronal seismology - is discussed and the applicability of this method for the estimation of coronal magnetic field, transport coefficients, fine structuring and heating function is demonstrated.

443 citations

References
More filters
Journal ArticleDOI
01 Jan 1958-Gff
TL;DR: In this paper, Elastic Waves in Layered Media (ELMW) are used to describe the properties of layered media in a geologiska foreningen i Stockholm Forhandlingar.
Abstract: (1958). Elastic Waves in Layered Media. Geologiska Foreningen i Stockholm Forhandlingar: Vol. 80, No. 1, pp. 128-129.

1,687 citations

Book
12 Apr 2013

581 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the occurrence of magnetoacoustic surface waves at a single magnetic interface and consider in detail the case where one side of the interface is field-free.
Abstract: The solar atmosphere, from the photosphere to the corona, is structured by the presence of magnetic fields. We consider the nature of such inhomogeneity and emphasis that the usual picture of hydromagnetic wave propagation in a uniform medium may be misleading if applied to a structured field. We investigate the occurrence of magnetoacoustic surface waves at a single magnetic interface and consider in detail the case where one side of the interface is field-free. For such an interface, a slow surface wave can always propagate. In addition, a fast surface wave may propagate if the field-free medium is warmer than the magnetic atmosphere.

256 citations

Journal ArticleDOI
TL;DR: In this paper, the propagation of waves in a magnetic slab embedded in magnetic environment is investigated and possible modes of propagation are examined from the general dispersion relation, both analytically and numerically, for disturbances which are evanescent in the environment.
Abstract: The propagation of waves in a magnetic slab embedded in a magnetic environment is investigated. The possible modes of propagation are examined from the general dispersion relation, both analytically and numerically, for disturbances which are evanescent in the environment. Approximate dispersion relations governing propagation in a slender slab of field are derived both from the general dispersion relation and from an application of the slender flux tube approximation.Several different situations, representative of both photospheric and coronal conditions, are considered. In general, the structures are found to support both fast and slow, body and surface, waves. Under coronal conditions, for two dimensional propagation, disturbances propagate as fast and slow body waves. The fast body waves are analogous to the ducted shear waves of seismology (Love waves).

247 citations