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Characteristics of magnetoacoustic sausage modes

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Inglis, Andrew R., Van Doorsselaere, Tom, Brady, Christopher S. and Nakariakov, Valery M.. (2009) Characteristics of magnetoacoustic sausage modes. Astronomy & Astrophysics, Vol.503 (No.2). pp. 569-675. ISSN 0004-6361

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Official URL: http://dx.doi.org/10.1051/0004-6361/200912088

Abstract

Aims: We perform an advanced study of the fast magnetoacoustic sausage oscillations of coronal loops in the context of MHD coronal seismology to establish the dependence of the sausage mode period and cut-off wavenumber on the plasma-$\beta$ of the loop-filling plasma. A parametric study of the ratios for different harmonics of the mode is also carried out. Methods: Full magnetohydrodynamic numerical simulations were performed using Lare2d, simulating hot, dense loops in a magnetic slab environment. The symmetric Epstein profile and a simple step-function profile were both used to model the density structure of the simulated loops. Analytical expressions for the cut-off wavenumber and the harmonic ratio between the second longitudinal harmonic and the fundamental were also examined. Results: It was established that the period of the global sausage mode is only very weakly dependent on the value of the plasma-$\beta$ inside a coronal loop, which justifies the application of this model to hot flaring loops. The cut-off wavenumber kc for the global mode was found to be dependent on both internal and external values of the plasma-$\beta$, again only weakly. By far the most important factor in this case was the value of the density contrast ratio between the loop and the surroundings. Finally, the deviation of the harmonic ratio P1/2P2 from the ideal non-dispersive case was shown to be considerable at low k, again strongly dependent on plasma density. Quantifying the behaviour of the cut-off wavenumber and the harmonic ratio has significant applications to the field of coronal seismology.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Magnetohydrodynamics -- Research, Solar wind, Sun -- Corona, Solar oscillations, Solar flares
Journal or Publication Title:	Astronomy & Astrophysics
Publisher:	EDP Sciences
ISSN:	0004-6361
Date:	August 2009
Volume:	Vol.503
Number:	No.2
Page Range:	pp. 569-675
Identification Number:	10.1051/0004-6361/200912088
Status:	Peer Reviewed
Access rights to Published version:	Restricted or Subscription Access
Funder:	Seventh Framework Programme (European Commission) (FP7/2007-2013), Science and Technology Facilities Council (Great Britain) (STFC)
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URI:	http://wrap.warwick.ac.uk/id/eprint/2332