Oscillations of coronal loops and second pulsations of solar radio emission

Kopylova, Yu. G.; Melnikov, Alexander; Stepanov, A. V.; Tsap, Yu. T.; Goldvarg, T. B.

doi:10.1134/s1063773707100088

Cited by 53 publications

(72 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The main properties of the sausage mode are derived from the straight cylinder or slab model. Clearly, the slab and the cylindrical cases are not identical, as has been discussed in Kopylova et al (2007). In particular, Terradas et al (2006) demonstrated the important difference in the wave leaking between these geometries.…”

Section: Introductionmentioning

confidence: 95%

Characteristics of magnetoacoustic sausage modes

Inglis¹,

Doorsselaere²,

Brady³

et al. 2009

A&A

View full text Add to dashboard Cite

Aims. We perform an advanced study of the fast magnetoacoustic sausage oscillations of coronal loops in the context of MHD coronal seismology to establish the dependence of the sausage mode period and cut-off wavenumber on the plasma-β of the loopfilling plasma. A parametric study of the ratios for different harmonics of the mode is also carried out. Methods. Full magnetohydrodynamic numerical simulations were performed using Lare2d, simulating hot, dense loops in a magnetic slab environment. The symmetric Epstein profile and a simple step-function profile were both used to model the density structure of the simulated loops. Analytical expressions for the cut-off wavenumber and the harmonic ratio between the second longitudinal harmonic and the fundamental were also examined. Results. It was established that the period of the global sausage mode is only very weakly dependent on the value of the plasma-β inside a coronal loop, which justifies the application of this model to hot flaring loops. The cut-off wavenumber k c for the global mode was found to be dependent on both internal and external values of the plasma-β, again only weakly. By far the most important factor in this case was the value of the density contrast ratio between the loop and the surroundings. Finally, the deviation of the harmonic ratio P 1 /2P 2 from the ideal non-dispersive case was shown to be considerable at low k, again strongly dependent on plasma density. Quantifying the behaviour of the cut-off wavenumber and the harmonic ratio has significant applications to the field of coronal seismology.

show abstract

Section: Introductionmentioning

confidence: 95%

Characteristics of magnetoacoustic sausage modes

Inglis¹,

Doorsselaere²,

Brady³

et al. 2009

A&A

View full text Add to dashboard Cite

show abstract

“…Moreover, because of their mild density contrast, AR loops are unlikely to support observable leaky modes either because, as estimated by Zaitsev & Stepanov (1975;also Eq. (6) in Kopylova et al 2007) for static loops with a step-function density distribution, in the thin-tube limit the ratio of the damping time to wave period τ/P is approximately (ρ 0 /ρ e )/π 2 , which evaluates to 1 for AR loops. Damped oscillations with such low-quality factors would be difficult to detect.…”

Section: Numerical Resultsmentioning

confidence: 99%

“…A further increase in L leads the sausage oscillations into the leaky regime, where P turns out to increase with L as well and shows saturation in the thin-tube limit (L/a 1). This behavior of sausage mode periods was analytically shown by Zaitsev & Stepanov (1975);Vasheghani Farahani et al (2014), and numerically demonstrated both via analysing the relevant dispersion diagrams (Kopylova et al 2007) and by solving the problem as an initial-boundary value one (Pascoe et al 2007a;Inglis et al 2009;Nakariakov et al 2012).…”

Section: Introductionmentioning

confidence: 97%

“…Those with axial wavenumbers larger than a cutoff k c correspond to the trapped regime with the oscillations confined in the loop. The leaky regime arises when the opposite is true, and the sausage modes are subject to damping by radiating their energy into the surrounding fluid (Zaitsev & Stepanov 1975;Kopylova et al 2007). However, that a sausage mode is in the leaky regime does not necessarily mean that it is not observationally accessible, provided that the quality factor Q = τ/P is sufficiently high, where τ and P denote the damping time and period, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…However, that a sausage mode is in the leaky regime does not necessarily mean that it is not observationally accessible, provided that the quality factor Q = τ/P is sufficiently high, where τ and P denote the damping time and period, respectively. In the idealized case where the parameters of the loop (denoted by the subscript 0) and its surroundings (subscript ∞) are piece-wise constant, both k c (Edwin & Roberts 1983) and Q (Kopylova et al 2007) turn out to depend primarily on the density contrast ρ 0 /ρ ∞ in a low beta environment. Regarding standing sausage modes, the wavenumber cutoff k c corresponds to a critical loop length-to-radius ratio (L/a) cutoff , which separates standing modes into trapped and leaky ones.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Standing sausage modes in coronal loops with plasma flow

Chen

Xia

et al. 2014

A&A

View full text Add to dashboard Cite

Context. Magnetohydrodynamic waves are important for diagnosing the physical parameters of coronal plasmas. Field-aligned flows appear frequently in coronal loops. Aims. We examine the effects of transverse density and plasma flow structuring on standing sausage modes trapped in coronal loops, and examine their observational implications in the context of coronal seismology. Methods. We model coronal loops as straight cold cylinders with plasma flow embedded in a static corona. An eigen-value problem governing propagating sausage waves is formulated and its solutions are employed to construct standing modes. Two transverse profiles are distinguished, and are called profiles E and N. A parameter study is performed on the dependence of the maximum period P max and cutoff length-to-radius ratio (L/a) cutoff in the trapped regime on the density parameters (ρ 0 /ρ ∞ and profile steepness p) and the flow parameters (its magnitude U 0 and profile steepness u). Results. For either profile, introducing a flow reduces P max obtainable in the trapped regime relative to the static case. The value of P max is sensitive to p for profile N, but is insensitive to p for profile E. By far the most important effect a flow introduces is to reduce the capability for loops to trap standing sausage modes: (L/a) cutoff may be substantially reduced in the case with flow relative to the static one. In addition, (L/a) cutoff is smaller for a stronger flow, and for a steeper flow profile when the flow magnitude is fixed. Conclusions. If the density distribution can be described by profile N, then measuring the sausage mode period can help deduce the density profile steepness. However, this practice is not feasible if profile E more accurately describes the density distribution. Furthermore, even field-aligned flows with magnitudes substantially smaller than the ambient Alfvén speed can make coronal loops considerably less likely to support trapped standing sausage modes.

show abstract