Transverse Loop Oscillations via Vortex Shedding: A Self-oscillating Process

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 Alfvenic 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.

Automated summary

This study explores the excitation mechanism of transverse oscillations in coronal loops, suggesting it may be caused by self-sustaining Alfvenic vortex shedding. The excited frequencies of these oscillations depend on the flow speed and loop characteristics, leading to the consideration of this mechanism as a self-oscillating process. The nearly constant amplitudes of the excited oscillations could explain the phenomena of decay-less oscillations in coronal loops.