2021/10/19 by Mingzhe Guo, Bo Li, Mijie Shi
Physics and Astronomy · #Astrophysics #Classical mechanics #Coronal loop #Coronal mass ejection #Coronal plane #Flare #Ionosphere and magnetosphere dynamics #Magnetic field #Magnetohydrodynamics #Mechanics #Physics #Quantum mechanics #Rotational symmetry #Solar and Space Plasma Dynamics #Solar flare #Solar wind #Stellar, planetary, and galactic studies #Transverse plane #astro-ph.SR
paper · pdf · doi:10.3847/2041-8213/ac30e3
Accepted for publication in ApJ Letters
arxiv created 2021/10/19 · openalex publication_date 2021/11/01 · arxiv updated 2021/11/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Abstract Fast sausage modes (FSMs) in flare loops have long been invoked to account for rapid quasi-periodic pulsations (QPPs) with periods of order seconds in flare lightcurves. However, most theories of FSMs in solar coronal cylinders assume a perfectly axisymmetric equilibrium, an idealized configuration apparently far from reality. In particular, it remains to be examined whether FSMs exist in coronal cylinders with fine structures. Working in the framework of ideal magnetohydrodynamics (MHD), we numerically follow the response to an axisymmetric perturbation of a coronal cylinder for which a considerable number of randomly distributed fine structures are superposed on an axisymmetric background. The parameters for the background component are largely motivated by the recent IRIS identification of a candidate FSM in Fe xxi 1354 Å observations. We find that the composite cylinder rapidly settles to an oscillatory behavior largely compatible with a canonical trapped FSM. This happens despite that kink-like motions develop in the fine structures. We further synthesize the Fe xxi 1354 Å emissions, finding that the transverse Alfvén time characterizes the periodicities in the intensity, Doppler shift, and Doppler width signals. Distinct from the case without fine structuring, a nonvanishing Doppler shift is seen even at the apex. We conclude that density-enhanced equilibria need not be strictly axisymmetric to host FSM-like motions in general, and FSMs remain a candidate interpretation for rapid QPPs in solar flares.