Abstract
We 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.
Highlights
Kink oscillations of coronal magnetic tubes were first observed by the Transition Region and Coronal Explorer (TRACE) mission in 1998
In this article we studied kink oscillations of a magnetic tube with siphon flow
Siphon flow has constant velocity parallel to the magnetic field, and it is confined to the tube core
Summary
Kink oscillations of coronal magnetic tubes were first observed by the Transition Region and Coronal Explorer (TRACE) mission in 1998. One more possible mechanism of excitation of kink waves in coronal magnetic tubes is the instability caused by the presence of a flow. To our knowledge the excitation of standing kink waves in magnetic-flux tubes in the solar corona by the KH instability has not been studied. After Ruderman and Roberts (2002) and Goossens, Andries, and Aschwanden (2002) showed that resonant absorption adequately explains the observed damping of coronal-loop kink oscillations and can be used to obtain seismological information about the transverse structure of coronal loops, this mechanism became especially popular in solar physics (see, e.g., Goossens, Erdélyi, and Ruderman, 2011). Bahari, Petrukhin, and Ruderman (2020) studied the resonant instability of propagating kink waves in magnetic tubes with flow with the application to waves in spicules and filaments in the solar atmosphere.
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