Transverse loop oscillations via vortex shedding: a self oscillating process

TL;DR

This paper demonstrates through 3D simulations that vortex shedding caused by background flows can excite transverse oscillations in coronal loops, potentially explaining observed decay-less waves and enhancing coronal seismology diagnostics.

Contribution

First to show in 3D simulations that vortex shedding can self-sustain transverse oscillations in coronal loops due to background flows.

Findings

Vortex shedding can generate transverse oscillations in coronal loops.

The excited frequencies depend on flow speed and loop characteristics.

Oscillation amplitudes are near constant and comparable to observed decay-less waves.

Abstract

Identifying the underlying mechanisms behind the excitation of transverse oscillations in coronal loops is essential for their role as diagnostic tools in coronal seismology and their potential use as wave heating mechanisms of the solar corona. In this paper, we explore the concept of these transverse oscillations being excited through a self-sustaining process, caused by Alfv\'{e}nic vortex shedding from strong background flows interacting with coronal loops. We show for the first time in 3D simulations that vortex shedding can generate transverse oscillations in coronal loops, in the direction perpendicular to the flow due to periodic "pushing" by the vortices. By plotting the power spectral density we identify the excited frequencies of these oscillations. We see that these frequencies are dependent both on the speed of the flow, as well as the characteristics of the oscillating loop. This, in addition to the fact that the background flow is constant and not periodic, makes us treat this as a self-oscillating process. Finally, the amplitudes of the excited oscillations are near constant in amplitude, and are comparable with the observations of decay-less oscillations. This makes the mechanism under consideration a possible interpretation of these undamped waves in coronal loops.