Periods and damping rates of fast sausage oscillations in multi-shelled coronal loops

Abstract

Standing sausage modes are important in interpreting quasi-periodic pulsations in the lightcurves of solar flares. Their periods and damping times play an important role in seismologically diagnosing key parameters like the magnetic field strength in regions where flare energy is released. Usually such applications are based on theoretical results neglecting unresolved fine structures in magnetized loops. However, the existence of fine structuring is suggested on both theoretical and observational grounds. Adopting the framework of cold magnetohydrodynamics (MHD), we model coronal loops as magnetized cylinders with a transverse equilibrium density profile comprising a monolithic part and a modulation due to fine structuring in the form of concentric shells. The equation governing the transverse velocity perturbation is solved with an initial-value-problem approach, and the effects of fine structuring on the periods $P$ and damping times $\tau$ of global, leaky, standing sausage modes are examined. A parameter study shows that fine structuring, be it periodically or randomly distributed, brings changes of only a few percent to $P$ and $\tau$ when there are more than about ten shells. The monolithic part, its steepness in particular, plays a far more important role in determining $P$ and $\tau$. We conclude that when measured values of $P$ and $\tau$ of sausage modes are used for seismological purposes, it is justified to use theoretical results where the effects due to fine structuring are neglected.

15 pages, 6 figures, accepted for publication in Solar Physics

References in corpus (7)

• Structure of solar coronal loops: from miniature to large-scale
• Analytic approximate seismology of transversely oscillating coronal loops
• Observations of Active Region Loops with the EUV Imaging Spectrometer on Hinode
• High Spatial Resolution Observations of Loops in the Solar Corona
• Characteristics of magnetoacoustic sausage modes
• Evolution of fast magnetoacoustic pulses in randomly structured coronal plasmas
• Effects of field-aligned flows on standing kink and sausage modes supported by coronal loops

Cited by in corpus (13)

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• Magnetohydrodynamic Fast Sausage Waves in the Solar Corona
• Inferring flare loop parameters with measurements of standing sausage modes
• Standing Sausage Modes In Nonuniform Magnetic Tubes: An Inversion Scheme For Inferring Flare Loop Parameters
• A Statistical Study of Short-period Decayless Oscillations of Coronal Loops in an Active Region
• Impulsively Generated Wave Trains in Coronal Structures: I. Effects of Transverse Structuring on Sausage Waves in Pressureless Tubes
• Impulsively generated wave trains in coronal structures: II. Effects of transverse structuring on sausage waves in pressureless slabs
• Fast sausage modes in magnetic tubes with continuous transverse profiles: effects of a finite plasma beta
• Effect of a sausage oscillation on radio zebra-pattern structures in a solar flare
• Propagating Slow Sausage Waves in a Sunspot Observed by the New Vacuum Solar Telescope
• Non-equilibrium Ionization Effects on Extreme-Ultraviolet Emissions Modulated by Standing Sausage Modes in Coronal Loops
• Fast Sausage Oscillations in Coronal Loops with Fine Structures
• Spatial damping of propagating sausage waves in coronal cylinders