Year: 2020
Type: article
Abstract: In this paper, we study propagating and standing magnetohydrodynamic kink waves in a magnetically twisted and flowing flux tube. The plasma flow is in the direction of the magnetic field; outside the tube, the magnetic field lines are purely longitudinal. The plasma density is constant both inside and outside the tube, and all stationary quantities vary abruptly at the tube boundary. Using the thin tube and weak twist approximations, the dispersion relation, which determines the dependence of the oscillation frequency on the wavenumber and the stationary quantities of the tube, is found. It is shown that the oscillation frequency of the propagating forward (backward) waves increases (decreases) as the flow speed increases; also, the increase in the magnetic twist increases the oscillation frequency of both forward and backward propagating waves. For very weak magnetic twist, the oscillation frequency of both fundamental mode and first overtone standing waves decreases with increasing flow speed. Our results show that if only the plasma flow or magnetic twist is present in the flux tube, the period ratio P 1/P 2 of the fundamental mode to the first overtone of the standing kink waves is equal to 2, but if both the plasma flow and magnetic twist are present in the flux tube, the period ratio can be smaller than 2 and support some observational cases. The asymmetry of the wave about the apex point is not affected much by the magnetic twist, but the magnetic twist causes an overestimation of both the flow speed and kink speed of the coronal loop.
Source: The Astrophysical Journal
Authors: Karam Bahari, Zeynab Jahan
Institution: Razi University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W3103045752