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Quasi-periodic wiggles of microwave zebra structures in a solar flare  

Valery Nakariakov   Submitted: 2013-09-23 10:03

Quasi-periodic wiggles of microwave zebra pattern structures with period range from about 0.5 s to 1.5 s are found in a X-class solar flare on 2006 December 13 at the 2.6-3.8 GHz with the Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou). Periodogram and correlation analysis show that the wiggles have two-three significant periodicities and almost in phase between stripes at different frequency. The Alfvén speed estimated from the zebra pattern structures is about 700 km s-1. We obtain the spatial size of the waveguiding plasma structure to be about 1 Mm with the detected period of about 1 s. It suggests the ZP wiggles can be associated with the fast magnetoacoustic oscillations in the flaring active region. The lack of a significant phase shift between wiggles of different stripes suggests that the ZP wiggles are caused by a standing sausage oscillation.

Authors: Sijie Yu, V. M. Nakariakov, L. A. Selzer, Baolin Tan and Yihua Yan
Projects: None

Publication Status: ApJ (accepted)
Last Modified: 2013-09-25 17:56
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Decay-less kink oscillations in coronal loops  

Valery Nakariakov   Submitted: 2013-08-22 14:49

Kink oscillations of coronal loops in an off-limb active region are detected with the Imaging Assembly Array (AIA) instruments of the Solar Dynamics Observatory (SDO) at 171~AA. We aim to measure periods and amplitudes of kink oscillations of different loops and to determinate the evolution of the oscillation phase along the oscillating loop. Oscillating coronal loops were visually identified in the field of view of SDO/AIA and STEREO/EUVI-A: the loop length was derived by three-dimensional analysis. Several slits were taken along the loops to assemble time-distance maps. We identified oscillatory patterns and retrieved periods and amplitudes of the oscillations. We applied the cross-correlation technique to estimate the phase shift between oscillations at different segments of oscillating loops. We found that all analysed loops show low-amplitude undamped transverse oscillations. Oscillations periods of loops in the same active region range from 2.5 to 11 min, and are different for different loops. The displacement amplitude is lower than 1~Mm. The oscillation phase is constant along each analysed loop. The spatial structure of the phase of the oscillations corresponds to the fundamental standing kink mode. We conclude that the observed behaviour is consistent with the empirical model in terms of a damped harmonic resonator affected by a non-resonant continuously operating external force.

Authors: S.A. Anfinogentov, G. Nistico, V. M. Nakariakov
Projects: SDO-AIA

Publication Status: A&A (accepted)
Last Modified: 2013-08-22 14:49
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Sausage oscillations of coronal plasma structures  

Valery Nakariakov   Submitted: 2012-10-30 16:08

Dependence of the period of sausage oscillations of coronal loops on its length and the radial profile depth and steepness is determined. We performed a parametric study of linear axisymmetric fast magnetoacoustic (sausage) oscillations of coronal loops modelled as a field-aligned low-beta plasma cylinder with a smooth inhomogeneity of the plasma density in the radial direction. The density decreases smoothly in the radial direction. Sausage oscillations are impulsively excited by a perturbation of the radial velocity, localised at the cylinder axis and having a harmonic dependence on the longitudinal coordinate. The initial perturbation results either in a leaky or trapped sausage oscillation, depending upon whether the longitudinal wavenumber is smaller or greater than a cut-off value, respectively. The period of the sausage oscillations was found to always grow with the increase in the longitudinal wavelength, with the saturation of this dependence in the long-wavelength limit. Deeper and steeper radial profiles of the Alfvén speed correspond to more efficient trapping of sausage modes: the cutoff value of the wavelength increases with the steepness and the density (or Alfvén speed) contrast ratio. In the leaky regime, the period is always longer than the period of a trapped mode of a shorter wavelength in the same cylinder. For shallow profiles of the density and shorter wavelengths, the period grows with the wavelength. In the long wavelength limit, the period becomes independent of the wavelength, and increases with the depth and steepness of the radial profile of the Alfvén speed.

Authors: Nakariakov, V.M., Hornsey, C., Melnikov, V.F.
Projects: None

Publication Status: accepted
Last Modified: 2012-10-30 19:45
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Slow Magnetoacoustic Waves in Two-Ribbon Flares  

Valery Nakariakov   Submitted: 2011-02-24 11:05

We demonstrate that disturbances observed to propagate along the axis of the arcade in two-ribbon solar flares at the speed of a few tens km s-1, well below the Alfvén and sound speeds, can be interpreted in terms of slow magnetoacoustic waves. The waves can propagate across the magnetic field, parallel to the magnetic neutral line, because of the wave-guiding effect due to the reflection from the footpoints. The perpendicular group speed of the perturbation is found to be a fraction of the sound speed, which is consistent with observations. The highest value of the group speed grows with the increase in the ratio of the sound and Alfvén speeds. For a broad range of parameters, the highest value of the group speed corresponds to the propagation angle of 25-28 degrees to the magnetic field. This effect can explain the temporal and spatial structure of quasi-periodic pulsations observed in two-ribbon flares.

Authors: Nakariakov, V.M., Zimovets, I.V.
Projects: None

Publication Status: ApJ L, accepted
Last Modified: 2011-02-24 19:33
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Oscillatory processes in solar flares  

Valery Nakariakov   Submitted: 2010-10-05 07:21

Electromagnetic (radio, visible-light, UV, EUV, X-ray and gamma-ray) emission generated by solar and stellar flares often contains pronounced quasi-periodic pulsations (QPP). Physical mechanisms responsible for the generation of long-period QPP (with the periods longer than one second) are likely to be associated with MHD processes. The observed modulation depths, periods and anharmonicity of QPP suggest that they can be linked with some kind of MHD auto-oscillations, e.g. an oscillatory regime of magnetic reconnection. Such regimes, of both spontaneous and induced nature, have been observed in resistive-MHD numerical simulations. The oscillations are essentially nonlinear and non-stationary. We demonstrate that a promising novel method for their analysis is the Empirical Mode Decomposition technique.

Authors: Authors: V.M. Nakariakov, A.R. Inglis, I.V. Zimovets, C. Foullon, E. Verwichte, R. Sych, I. N. Myagkova
Projects: RHESSI

Publication Status: Plasma Phys. Controlled Fusion (in press)
Last Modified: 2010-10-05 08:00
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Quasi-periodic pulsations in the gamma-ray emission of a solar flare  

Valery Nakariakov   Submitted: 2009-12-02 07:57

Quasi-periodic pulsations (QPP) of gamma-ray emission with a period of about 40 s are found in a single loop X-class solar flare on 2005 January 01 at photon energies up to 2-6 MeV with the SOlar Neutrons and Gamma-rays (SONG)experiment aboard the CORONAS-F mission. The oscillations are also found to be present in the microwave emission detected with the Nobeyama Radioheliograph, and in the hard X-ray and low energy gamma-ray channels of RHESSI. Periodogram and correlation analysis show that the 40 s QPP of microwave, hard X-ray and gamma-ray emission are almost synchronous in all observation bands. Analysis of the spatial structure of hard X-ray and low energy (80-225 keV) gamma-ray QPP with RHESSI reveal synchronous while asymmetric QPP at both footpoints of the flaring loop. The difference between the averaged hard X-ray fluxes coming from the two footpoint sources is found to oscillate with a period of about 13 s for five cycles in the highest emission stage of the flare. The proposed mechanism generating the 40 s QPP is a triggering of magnetic reconnection by a kink oscillation in a nearby loop. The 13 s periodicity could be produced by the second harmonics of the sausage mode of the flaring loop.

Authors: Nakariakov, V.M., Foullon, C., Myagkova, I.N., Inglis, A.R.
Projects: None

Publication Status: ApJL, in press
Last Modified: 2009-12-02 17:20
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The possible role of vortex shedding in the excitation of kink-mode oscillations in the solar corona  

Valery Nakariakov   Submitted: 2009-06-11 10:10

We propose a model for the excitation of horizontally polarised transverse (kink) magnetoacoustic oscillations of solar coronal loops by upflows associated with coronal mass ejections. If the magnetic field in the plasma that is dragged in the vertical direction by the flow is parallel to the loop, the phenomenon of vortex shedding causes the appearance of a quasi-periodic horizontal force that is applied to alternating sides of the loop. The period of the force is determined by the flow speed and the loop?s minor radius. The oscillations are excited the most effectively when the force is in resonance with the natural frequency of the kink oscillations. This model can explain the selectivity of the excitation of the oscillations and the initial growth of the oscillation amplitude.

Authors: V. M. Nakariakov, M. J. Aschwanden, and T. Van Doorsselaere
Projects: None

Publication Status: A&A (in press)
Last Modified: 2009-06-11 11:24
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MHD oscillations in solar and stellar coronae: Current results and perspectives  

Valery Nakariakov   Submitted: 2007-05-02 03:12

Wave and oscillatory activity is observed with modern imaging and spectral instruments in the visible light, EUV, X-ray and radio bands in all parts of the solar corona. Magnetohydrodynamic (MHD) wave theory gives satisfactory interpretation of these phenomena in terms of MHD modes of coronal structures. The paper reviews the current trends in the observational study of coronal oscillations, recent development of theoretical modelling of MHD wave interaction with plasma structures, and implementation of the theoretical results for the mode identification. Also the use of MHD waves for remote diagnostics of coronal plasmas is discussed. In particular, the applicability of this method to the estimation of the coronal magnetic field is demonstrated.

Authors: V.M. Nakariakov
Projects: None

Publication Status: J. Adv. Space Res. (in press)
Last Modified: 2007-05-02 05:54
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Coronal periodmaps. Automated detection of wave and oscillatory phenomena in coronal imaging data.  

Valery Nakariakov   Submitted: 2007-03-15 09:49

The search for signatures of wave and oscillatory processes in the solar corona in the data obtained with imaging instruments can be automated using the periodmap method. The method reduces a three-dimensional data cube to a two-dimensional map of the analysed field-of-view. The map reveals the presence and distribution of the most pronounced frequencies in the power spectrum of the time signal recorded at spatial pixels. We demonstrate the applicability of this method as a pre-analysis tool with the use of TRACE EUV coronal data, which contain examples of transverse and longitudinal oscillations of coronal loops. The main advantage of using periodmaps over other possible (more sophisticated) pre-analysis tools, such as wavelet analysis, is its robustness and efficiency (both in speed and computational power). The method can be implemented in the Hinode/XRT and SDO/AIA data pre-analysis.

Authors: Nakariakov, V.M., King, D.B.
Projects: None

Publication Status: Solar Physics (accepted)
Last Modified: 2007-03-15 10:11
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Quasi-periodic modulation of solar and stellar flaring emission by magnetohydrodynamic oscillations in a nearby loop  

Valery Nakariakov   Submitted: 2006-02-24 07:26

We propose a new model for quasi-periodic modulation of solar and stellar flaring emission. Fast magnetoacoustic oscillations of a non-flaring loop can interact with a nearby flaring active region. This interaction occurs when part of the oscillation situated outside the loop reaches the regions of steep gradients in magnetic field within an active region and produce periodic variations of electric current density. The modulation depth of these variations is a few orders of magnitude greater than the amplitude of the driving oscillation. The variations of the current can induce current-driven plasma micro-instabilities and thus anomalous resistivity. This can periodically trigger magnetic reconnection, and hence acceleration of charged particles, producing quasi-periodic pulsations of X-ray, optical and radio emission at the arcade footpoints.

Authors: V.M. Nakariakov, C. Foullon, E. Verwichte, N.P. Young
Projects:

Publication Status: A&A (in press)
Last Modified: 2006-02-24 07:29
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Modulation of gyrosynchrotron emission in solar and stellar flares by slow magnetoacoustic oscillations  

Valery Nakariakov   Submitted: 2005-09-27 07:17

Gyrosynchrotron emission generated by non-thermal electrons in solar and stellar coronal flares can be efficiently modulated by slow magnetoacoustic oscillations in the flaring loops. The modulation mechanism is based upon the perturbation of the efficiency of Razin suppression of optically thin gyrosynchrotron emission. The modulation of the emission is in anti-phase with the density perturbation in the slow wave. The observed emission modulation depth can be up to an order of magnitude higher than the slow wave amplitude. The modulation is more pronounced at lower frequencies. Observations with spatial resolution together with the analysis of the modulation frequency are shown to be sufficient to provide the information sufficient for the mode identification.

Authors: V.M. Nakariakov, V.F. Melnikov
Projects: None

Publication Status: A&A (in press)
Last Modified: 2005-09-27 07:17
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Acoustic Oscillations in Solar and Stellar Flaring Loops  

Valery Nakariakov   Submitted: 2003-12-22 02:58

Evolution of a coronal loop in response to an impulsive energy release is numerically modelled. It is shown that the loop density evolution curves exhibit quasi-periodic perturbations with the periods given approximately by the ratio of the loop length to the average sound speed, associated with the second standing harmonics of an acoustic wave. The density perturbations have a maximum near the loop apex. The corresponding field-aligned flows have a node near the apex. We suggest that the quasi-periodic pulsations with periods in the range 10-300 s, frequently observed in flaring coronal loops in the radio, visible light and X-ray bands, may be produced by the second standing harmonic of the acoustic mode.

Authors: V.M. Nakariakov, D. Tsiklauri, A. Kelly, T.D. Arber, M.J. Aschwanden
Projects:

Publication Status: Astron.Astrophys. 414 (2004) L25-L28
Last Modified: 2010-12-14 09:29
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Time signatures of impulsively generated coronal fast wave trains  

Valery Nakariakov   Submitted: 2003-12-22 02:54

Impulsively-generated short-period fast magnetoacoustic wave trains, guided by solar and stellar coronal loops are numerically modelled. In the developed stage of the evolution, the wave trains have a characteristic quasi-periodic signature. The quasi-periodicity results from the geometrical dispersion of the guided fast modes, determined by the transverse profile of the loop. A typical feature of the signature is a lqlq tadpole'' wavelet spectrum: a narrow spectrum tail precedes a broad band head. The instantaneous period of the oscillations in the wave train decreases gradually with time. The period and the spectral amplitude evolution are shown to be determined by the steepness of the transverse density profile and the density contrast ratio in the loop. The propagating wave trains recently discovered with the SECIS instrument are pointed out to have similar wavelet spectral features, which strengthens the interpretation of SECIS results as guided fast wave trains.

Authors: V.M. Nakariakov, T.D. Arber, C.E. Ault, A.C. Katsiyannis, D.R. Williams, F.P. Keenan
Projects: None

Publication Status: MNRAS (in press)
Last Modified: 2003-12-22 02:54
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Global Sausage Modes of Coronal Loops  

Valery Nakariakov   Submitted: 2003-10-31 08:00

Sufficiently thick and dense coronal loops can support global sausage magnetoacoustic modes. We demonstrate that the oscillation period of this mode, calculated in the straight cylinder approximation, is determined by the length of the loop, not by its diameter, as it was previously assumed. The existence condition for this mode is the ratio of the loop length to its diameter to be less than about a half of the square root of the density contrast ratio. This mode has a maximum of the magnetic field perturbation at the loop apex and nodes at the footpoints. We demonstrate that the 14-17 s quasi-periodic pulsations, oscillating in phase at a loop apex and at its legs, observed with the Nobeyama Radioheliograph, are interpreted in terms of the global sausage mode.

Authors: V.M. Nakariakov, V.F. Melnikov and V.E. Reznikova
Projects: None

Publication Status: A&A in press
Last Modified: 2003-10-31 08:00
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Abstracts by Author
Do periods of decayless kink oscillations of solar coronal loops depend on noise?
Two-spacecraft detection of short-period decayless kink oscillations of solar coronal loops
Slow magnetoacoustic oscillations in stellar coronal loops
Kink oscillations of coronal loops
Excitation of negative energy surface magnetohydrodynamic waves in an incompressible cylindrical plasma
Oscillation of a small Halpha surge in a solar polar coronal hole
Properties of slow magnetoacoustic oscillations of solar coronal loops by multi-instrumental observations
Non-stationary quasi-periodic pulsations in solar and stellar flares
Quasi-periodic Pulsations in a Solar Microflare
Effect of local thermal equilibrium misbalance on long-wavelength slow magnetoacoustic waves
Comparison of damped oscillations in solar and stellar X-ray flares
Undamped transverse oscillations of coronal loops as a self-oscillatory process
Dependence of kink oscillation damping on the amplitude
Magnetohydrodynamic oscillations in the solar corona and Earth's magnetosphere: Towards consolidated understanding
Solar and Heliospheric Physics with the Square Kilometre Array
Excitation of kink oscillations of coronal loops: statistical study
Multi-mode quasi-periodic pulsations in a solar flare
Nonlinear slow magnetoacoustic waves in coronal plasma structures
Wave dynamics in a sunspot umbra
Sausage oscillations of coronal plasma slabs
Quasi-periodic wiggles of microwave zebra structures in a solar flare
Decay-less kink oscillations in coronal loops
Sausage oscillations of coronal plasma structures
Slow Magnetoacoustic Waves in Two-Ribbon Flares
Oscillatory processes in solar flares
Quasi-periodic pulsations in the gamma-ray emission of a solar flare
The possible role of vortex shedding in the excitation of kink-mode oscillations in the solar corona
MHD oscillations in solar and stellar coronae: Current results and perspectives
Coronal periodmaps. Automated detection of wave and oscillatory phenomena in coronal imaging data.
Quasi-periodic modulation of solar and stellar flaring emission by magnetohydrodynamic oscillations in a nearby loop
Modulation of gyrosynchrotron emission in solar and stellar flares by slow magnetoacoustic oscillations
Acoustic Oscillations in Solar and Stellar Flaring Loops
Time signatures of impulsively generated coronal fast wave trains
Global Sausage Modes of Coronal Loops

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