Characteristics of magnetoacoustic sausage modes
Inglis, Andrew R., Van Doorsselaere, Tom, Brady, Christopher S. and Nakariakov, V. M. (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
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|
|Official Date:||August 2009|
|Page Range:||pp. 569-675|
|Access rights to Published version:||Restricted or Subscription Access|
|Funder:||Seventh Framework Programme (European Commission) (FP7), Science and Technology Facilities Council (Great Britain) (STFC)|
Andries, J., Arregui, I., & Goossens, M. 2005, ApJ, 624, L57
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