scholarly journals Resonant Instability of Kink Oscillations in Magnetic Flux Tubes with Siphon Flow

Solar Physics ◽  
2021 ◽  
Vol 296 (6) ◽  
Author(s):  
Michael S. Ruderman ◽  
Nikolai S. Petrukhin
Keyword(s):  
Flow Velocity ◽  
Resonant Absorption ◽  
Tube Axis ◽  
Magnetic Tube ◽  
Transitional Layer ◽  
Threshold Velocity ◽  
Flux Tubes ◽  
Resonant Instability ◽  
Constant Magnitude ◽  
Magnetic Flux Tubes

AbstractWe study kink oscillations of a straight magnetic tube in the presence of siphon flows. The tube consists of a core and a transitional or boundary layer. The flow velocity is parallel to the tube axis, has constant magnitude, and confined in the tube core. The plasma density is constant in the tube core and it monotonically decreases in the transitional layer to its value in the surrounding plasma. We use the expression for the decrement/increment previously obtained by Ruderman and Petrukhin (Astron. Astrophys.631, A31, 2019) to study the damping and resonant instability of kink oscillations. We show that, depending on the magnitude of siphon-velocity, resonant absorption can cause either the damping of kink oscillations or their enhancement. There are two threshold velocities: When the flow velocity is below the first threshold velocity, kink oscillations damp. When the flow velocity is above the second threshold velocity, the kink oscillation amplitudes grow. Finally, when the flow velocity is between the two threshold velocities, the oscillation amplitudes do not change. We apply the theoretical result to kink oscillations of prominence threads. We show that, for particular values of thread parameters, resonant instability can excite these kink oscillations.

scholarly journals Effect of siphon flow on resonant damping of kink oscillations in magnetic flux tubes

2019 ◽  
Vol 631 ◽  
pp. A31 ◽  
Author(s):  
Michael S. Ruderman ◽  
Nikolai S. Petrukhin
Keyword(s):  
Magnetic Flux ◽  
Flow Velocity ◽  
Radial Dependence ◽  
Transitional Layer ◽  
Regular Perturbation ◽  
Flux Tubes ◽  
Velocity Amplitude ◽  
Velocity Magnitude ◽  
First Case ◽  
Magnetic Flux Tubes

The effect of siphon flow on kink oscillations of magnetic flux tubes is studied in the thin tube and thin boundary layer (TTTB) approximation. The presence of a transitional layer results in oscillation damping due to resonance absorption. To calculate the damping rate we use the regular perturbation method with the ratio of transitional layer thickness to tube radius as a small parameter. We found a dependence of the ratio of decrement to the oscillation frequency, γ/ω1, on the ratio, χ, of flow velocity magnitude to the Alfvén speed in the tube core. The general theoretical results are applied to a particular case where the density radial dependence in the transitional layer is linear. We consider two models. In the first model, the radial dependence of the velocity amplitude is such that the resonance in the transitional layer occurs where the flow velocity is zero. In the second model, the flow velocity is non-zero in the whole transitional layer. In both cases, γ/ω1 is an increasing function of χ. In the first case, the presence of flow can lead to an increase in γ/ω1 by more than a factor of two. In the second model, we only carry out the calculation in the case where the plasma density inside the tube is much larger than the density of the surrounding plasma. In this model, the effect of flow is less pronounced than in the first model, and the presence of flow can increase γ/ω1 by a factor of 0.25 at most. We discuss the application of the obtained results to coronal and prominence seismology. We conclude that while for typical values of velocity in coronal loops the effect of flow is weak, it can be quite substantial in prominence seismology.

Linear Visco-Resistive Computations of Magnetohydrodynamic Waves: I. The Code and Test Cases

1994 ◽  
Vol 144 ◽  
pp. 503-505
Author(s):  
R. Erdélyi ◽  
M. Goossens ◽  
S. Poedts
Keyword(s):  
Resonant Absorption ◽  
Numerical Code ◽  
Mhd Waves ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Element Discretization ◽  
Flux Tubes ◽  
Magnetohydrodynamic Waves ◽  
Viscosity Coefficients ◽  
Magnetic Flux Tubes

AbstractThe stationary state of resonant absorption of linear, MHD waves in cylindrical magnetic flux tubes is studied in viscous, compressible MHD with a numerical code using finite element discretization. The full viscosity tensor with the five viscosity coefficients as given by Braginskii is included in the analysis. Our computations reproduce the absorption rates obtained by Lou in scalar viscous MHD and Goossens and Poedts in resistive MHD, which guarantee the numerical accuracy of the tensorial viscous MHD code.

scholarly journals Resonant damping of kink oscillations of thin expanding magnetic tubes

2018 ◽  
Vol 615 ◽  
pp. A156 ◽  
Author(s):  
A. A. Shukhobodskiy ◽  
M. S. Ruderman
Keyword(s):  
Magnetic Flux ◽  
Oscillation Frequency ◽  
Density Variation ◽  
Magnetic Pressure ◽  
Transitional Region ◽  
Transitional Layer ◽  
Flux Tubes ◽  
Flux Function ◽  
Plasma Displacement ◽  
Magnetic Flux Tubes

We study the resonant damping of kink oscillations of thin expanding magnetic flux tubes. The tube consists of a core region and a thin transitional region at the tube boundary. The resonance occurs in this transitional layer where the oscillation frequency coincides with the local Alfvén frequency. Our investigation is based on the system of equations that we previously derived. This system is not closed because it contains the jumps of the magnetic pressure perturbation and plasma displacement across the transitional layer. We calculate these jumps and thus close the system. We then use it to determine the decrements of oscillation eigenmodes. We introduce the notion of homogeneous stratification. In accordance with this condition the ratio of densities in the tube core and outside the tube does not vary along the tube, while the density in the transitional layer can be factorised and written as a product of two function, one depending on the variable along the tube and the other on the magnetic flux function. Our main result is that, under the condition of homogeneous stratification, the ratio of the decrement to the oscillation frequency is independent of a particular form of the density variation along the tube. This ratio is also the same for all oscillation eigenmodes.

scholarly journals RESONANT ABSORPTION OF AXISYMMETRIC MODES IN TWISTED MAGNETIC FLUX TUBES

2016 ◽  
Vol 823 (2) ◽  
pp. 71 ◽  
Author(s):  
I. Giagkiozis ◽  
M. Goossens ◽  
G. Verth ◽  
V. Fedun ◽  
T. Van Doorsselaere
Keyword(s):  
Magnetic Flux ◽  
Resonant Absorption ◽  
Flux Tubes ◽  
Magnetic Flux Tubes

Topological Transformations in Isolated Straight Magnetic Flux Tubes

1998 ◽  
Vol 500 (2) ◽  
pp. 966-977 ◽  
Author(s):  
Sergey Bazdenkov ◽  
Tetsuya Sato
Keyword(s):  
Magnetic Flux ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
Topological Transformations

scholarly journals The Influence of Binarity on Stellar Activity

2006 ◽  
Vol 2 (S240) ◽  
pp. 442-452 ◽  
Author(s):  
Katalin Oláh
Keyword(s):  
Binary Systems ◽  
Magnetic Energy ◽  
Theoretical Calculations ◽  
Deep Convection ◽  
Magnetic Activity ◽  
Close Binary ◽  
Convective Envelope ◽  
Flux Tubes ◽  
Gravitational Forces ◽  
Magnetic Flux Tubes

AbstractActivity of late type stars is enhanced by fast rotation, which is maintained in nearly synchronized close binary systems. Magnetic activity originates in the deep convection zones of stars from where magnetic flux tubes emerge to their surfaces. The gravitational forces in binaries help the clustering of activity features giving rise to active longitudes. These preferred longitudes are observed in binaries from dwarfs to giants. Differential rotation is found in many active stars that are components of binary systems. If these binaries are circularized and nearly synchronized, then there will be a corotation latitude in their surfaces, and its position can be determined by observations and by theoretical calculations. Enhanced activity in binaries could have a reverse effect as well: strong magnetism in a binary component can modify the orbital period by the cyclic exchange of kinetic and magnetic energy in its convective envelope.

The Characteristics of Thin Magnetic Flux Tubes in the Lower Solar Atmosphere Observed byHinode/SOT in the G band and in Ca ii H Bright Points

2017 ◽  
Vol 851 (1) ◽  
pp. 42 ◽  
Author(s):  
Jianping Xiong ◽  
Yunfei Yang ◽  
Chunlan Jin ◽  
Kaifan Ji ◽  
Song Feng ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Solar Atmosphere ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
Lower Solar Atmosphere
Sign in / Sign up

Export Citation Format

Share Document