Standing sausage modes in coronal loops with plasma flow

Abstract

Magnetohydrodynamic waves are important for diagnosing the physical parameters of coronal plasmas. Field-aligned flows appear frequently in coronal loops.We examine the effects of transverse density and plasma flow structuring on standing sausage modes trapped in coronal loops, and examine their observational implications. We model coronal loops as straight cold cylinders with plasma flow embedded in a static corona. An eigen-value problem governing propagating sausage waves is formulated, its solutions used to construct standing modes. Two transverse profiles are distinguished, one being the generalized Epstein distribution (profile E) and the other (N) proposed recently in Nakariakov et al.(2012). A parameter study is performed on the dependence of the maximum period $P_{\max }$ and cutoff length-to-radius ratio $(L/a{)}_{\mathrm{cutoff}}$ in the trapped regime on the density parameters (${\rho }_0/{\rho }_{\infty }$ and profile steepness $p$) and flow parameters (magnitude $U_0$ and profile steepness $u$). For either profile, introducing a flow reduces $P_{\max }$ relative to the static case. $P_{\max }$ depends sensitively on $p$ for profile N but is insensitive to $p$ for profile E. By far the most important effect a flow introduces is to reduce the capability for loops to trap standing sausage modes: $(L/a{)}_{\mathrm{cutoff}}$ may be substantially reduced in the case with flow relative to the static one. If the density distribution can be described by profile N, then measuring the sausage mode period can help deduce the density profile steepness. However, this practice is not feasible if profile E better describes the density distribution. Furthermore, even field-aligned flows with magnitudes substantially smaller than the ambient Alfvén speed can make coronal loops considerably less likely to support trapped standing sausage modes.

11 pages, 9 figures, to appear in Astronomy & Astrophysics

References in corpus (9)

• MHD Waves and Coronal Seismology: an overview of recent results
• Observations of ubiquitous compressive waves in the Sun's chromosphere
• MHD Sausage Mode Oscillations in Coronal Loops
• Line-of-sight Effects on Observability of Kink and Sausage Modes in Coronal Structures with Imaging Telescopes
• Line-of-sight geometrical and instrumental resolution effects on intensity perturbations by sausage modes
• Characteristics of magnetoacoustic sausage modes
• Seismology of transversely oscillating coronal loops with siphon flows
• The period ratio for standing kink and sausage modes in solar structures with siphon flow. I. magnetized slabs
• Observations of Plasma Upflow in a Warm Loop with Hinode/EIS

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• Impulsively generated wave trains in coronal structures: II. Effects of transverse structuring on sausage waves in pressureless slabs
• 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
• Synthetic Emissions of the Fe XXI 1354 Å Line from Flare Loops Experiencing Fundamental Fast Sausage Oscillations
• Inference of Magnetic Field in the Coronal Streamer Invoking Kink Wave Motions generated by Multiple EUV Waves
• Effects of external flow on resonant absorption of coronal loop kink oscillations driven by an external fast wave: Selective excitation problem
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