Transverse loop oscillations via vortex shedding: a self oscillating process

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 Alfvénic 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.

8 pages, 8 figures, accepted for publication in ApJL

References in corpus (14)

• Persistent Doppler shift oscillations observed with HINODE/EIS in the solar corona: spectroscopic signatures of Alfvenic waves and recurring upflows
• Nonlinear Instability of kink oscillations due to shear motions
• Global maps of the magnetic field in the solar corona
• Fine strand-like structure in the solar corona from MHD transverse oscillations
• Heating by transverse waves in simulated coronal loops
• Modelling observed decay-less oscillations as resonantly enhanced Kelvin-Helmholtz vortices from transverse MHD waves and their seismological application
• Long-Period Intensity Pulsations in Coronal Loops Explained by Thermal Non-Equilibrium Cycles
• Excitation of decay-less transverse oscillations of coronal loops by random motions
• Amplitudes and energy fluxes of simulated decayless kink oscillations
• The First 3D Coronal Loop Model Heated by MHD Waves against Radiative Losses
• Magnetohydrodynamic Seismology of Quiet Solar Active Regions
• Generating transverse loop oscillations through a steady-flow driver
• Coronal loop transverse oscillations excited by different driver frequencies
• Evidence for Vortex Shedding in the Sun's Hot Corona