Longitudinal Magnetohydrodynamics Oscillations in Dissipative, Cooling Coronal Loops

Al-Ghafri, K. S.; Williamson, A.; Erdélyi, R.

doi:10.1088/0004-637x/786/1/36

Cited by 16 publications

(20 citation statements)

References 27 publications

(34 reference statements)

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“…Using this invariant he showed that cooling causes the amplification of kink oscillations. Similar results were obtained for longitudinal oscillations (see Al-Ghafri & Erdélyi 2013;Al-Ghafri et al 2014). Ruderman (2010) assumed that the density can vary along the loop, but it does not vary in the transverse direction.…”

Section: Introductionsupporting

confidence: 84%

Kink oscillations of cooling coronal loops with variable cross-section

Shukhobodskiy

Erdélyi

2017

A&A

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We study kink waves and oscillations in a thin expanding magnetic tube in the presence of flow. The tube consists of a core region and a thin transitional region at the tube boundary. In this region the plasma density monotonically decreases from its value in the core region to the value outside the tube. Both the plasma density and velocity of background flow vary along the tube and in time. Using the multiscale expansions we derive the system of two equations describing the kink oscillations. When there is no transitional layer the oscillations are described by the first of these two equations. We use this equation to study the effect of plasma density variation with time on kink oscillations of an expanding tube with a sharp boundary. We assume that the characteristic time of the density variation is much greater than the characteristic time of kink oscillations. Then we use the Wentzel-Kramer-Brillouin (WKB) method to derive the expression for the adiabatic invariant, which is the quantity that is conserved when the plasma density varies. The general theoretical results are applied to the kink oscillations of coronal magnetic loops. We consider an expanding loop with the half-circle shape and assume that the plasma temperature inside a loop decays exponentially with time. We numerically calculated the dependences of the fundamental mode frequency, the ratio of frequencies of the first overtone and fundamental mode, and the oscillation amplitude on time. We obtained that the oscillation frequency and amplitude increase and the frequency ratio decreases due to cooling. The amplitude increase is stronger for loops with a greater expansion factor. This effect is also more pronounced for higher loops. However, it is fairly moderate even for loops that are quite high.

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Section: Introductionsupporting

confidence: 84%

Kink oscillations of cooling coronal loops with variable cross-section

Shukhobodskiy

Erdélyi

2017

A&A

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“…Aschwanden & Terradas 2008). Morton & Erdélyi (2009, 2010 found that cooling results in the decrease of the period of the coronal loop kink oscillations, while similar results were found by Al-Ghafri et al (2014) for longitudinal oscillations. Ruderman (2011b) showed that cooling causes the amplification of coronal loop kink oscillations.…”

Section: Introductionsupporting

confidence: 60%

Resonant damping of kink oscillations of thin cooling and expanding coronal magnetic loops

Shukhobodskiy

Erdélyi

2018

A&A

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We have considered resonant damping of kink oscillations of cooling and expanding coronal magnetic loops. We derived an evolutionary equation describing the dependence of the oscillation amplitude on time. When there is no resonant damping, this equation reduces to the condition of conservation of a previously derived adiabatic invariant. We used the evolutionary equation describing the amplitude to study the competition between damping due to resonant absorption and amplification due to cooling. Our main aim is to investigate the effect of loop expansion on this process. We show that the loop expansion acts in favour of amplification. We found that, when there is no resonant damping, the larger the loop expansion the faster the amplitude growths. When the oscillation amplitude decays due to resonant damping, the loop expansion reduces the damping rate. For some values of parameters the loop expansion can fully counterbalance the amplitude decay and turn the amplitude evolution into amplification.

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“…MHD simulations by Ofman & Wang (2002) suggested that thermal conduction is the dominant wave damping mechanism enhanced by nonlinear effect. The role of other physical effects such as compressive viscosity, non-equilibrium ionization, shock dissipation, loop cooling, etc was also studied theoretically (see a review by Wang 2011;Ruderman 2013;Al-Ghafri et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Evidence of Thermal Conduction Suppression in a Solar Flaring Loop by Coronal Seismology of Slow-Mode Waves

Wang

Ofman

Sun

et al. 2015

ApJ

107

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Analysis of a longitudinal wave event observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) is presented. A time sequence of 131Å images reveals that a C-class flare occurred at one footpoint of a large loop and triggered an intensity disturbance (enhancement) propagating along it. The spatial features and temporal evolution suggest that a fundamental standing slow-mode wave could be set up quickly after meeting of two initial disturbances from the opposite footpoints. The oscillations have a period of ∼12 min and a decay time of ∼9 min. The measured phase speed of 500±50 km s −1 matches the sound speed in the heated loop of ∼10 MK, confirming that the observed waves are of slow mode. We derive the time-dependent temperature and electron density wave signals from six AIA extreme-ultraviolet (EUV) channels, and find that they are nearly in phase. The measured polytropic index from the temperature and density perturbations is 1.64 ± 0.08 close to the adiabatic index of 5/3 for an ideal monatomic gas. The interpretation based on a 1D linear MHD model suggests that the thermal conductivity is suppressed by at least a factor of 3 in the hot flare loop at 9 MK and above. The viscosity coefficient is determined by coronal seismology from the observed wave when only considering the compressive viscosity dissipation. We find that to interpret the rapid wave damping, the classical compressive viscosity coefficient needs to be enhanced by a factor of 15 as the upper limit.

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Longitudinal Magnetohydrodynamics Oscillations in Dissipative, Cooling Coronal Loops

Cited by 16 publications

References 27 publications

Kink oscillations of cooling coronal loops with variable cross-section

Kink oscillations of cooling coronal loops with variable cross-section

Resonant damping of kink oscillations of thin cooling and expanding coronal magnetic loops

Evidence of Thermal Conduction Suppression in a Solar Flaring Loop by Coronal Seismology of Slow-Mode Waves

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