Decayless Kink Oscillations Excited by Random Driving: Motion in Transitional Layer

Solar Physics. 2021. Vol. 296. Article 124.

Ruderman M. S., Petrukhin N., Pelinovsky E.

In this article we study the plasma motion in the transitional layer of a coronal loop randomly
driven at one of its footpoints in the thin-tube and thin-boundary-layer (TTTB) approximation. We introduce the average of the square of a random function with respect to time. This
average can be considered as the square of the oscillation amplitude of this quantity. Then
we calculate the oscillation amplitudes of the radial and azimuthal plasma displacement as
well as the perturbation of the magnetic pressure. We find that the amplitudes of the plasma
radial displacement and the magnetic-pressure perturbation do not change across the transitional layer. The amplitude of the plasma radial displacement is of the same order as the
driver amplitude. The amplitude of the magnetic-pressure perturbation is of the order of
the driver amplitude times the ratio of the loop radius to the loop length squared. The amplitude of the plasma azimuthal displacement is of the order of the driver amplitude times
Re1/6, where Re is the Reynolds number. It has a peak at the position in the transitional layer
where the local Alfvén frequency coincides with the fundamental frequency of the loop kink
oscillation. The ratio of the amplitude near this position and far from it is of the order of ,
where is the ratio of thickness of the transitional layer to the loop radius. We calculate the
dependence of the plasma azimuthal displacement on the radial distance in the transitional
layer in a particular case where the density profile in this layer is linear
 

Keywords: колебания, волны, устойчивость, stability, Sun, Солнце, плазма, waves, oscillations, plasma, magnetohydrodynamics, Магнитогидродинамика