Sausage oscillations of coronal plasma structures |
|
Valery Nakariakov Submitted: 2012-10-30 16:08
Dependence of the period of sausage oscillations of coronal loops on its length and the radial profile depth and steepness is determined. We performed a parametric study of linear axisymmetric fast magnetoacoustic (sausage) oscillations of coronal loops modelled as a field-aligned low-beta plasma cylinder with a smooth inhomogeneity of the plasma density in the radial direction. The density decreases smoothly in the radial direction. Sausage oscillations are impulsively excited by a perturbation of the radial velocity, localised at the cylinder axis and having a harmonic dependence on the longitudinal coordinate.
The initial perturbation results either in a leaky or trapped sausage oscillation, depending upon whether the longitudinal wavenumber is smaller or greater than a cut-off value, respectively. The period of the sausage oscillations was found to always grow with the increase in the longitudinal wavelength, with the saturation of this dependence in the long-wavelength limit. Deeper and steeper radial profiles of the Alfvén speed correspond to more efficient trapping of sausage modes: the cutoff value of the wavelength increases with the steepness and the density (or Alfvén speed) contrast ratio. In the leaky regime, the period is always longer than the period of a trapped mode of a shorter wavelength in the same cylinder.
For shallow profiles of the density and shorter wavelengths, the period grows with the wavelength. In the long wavelength limit, the period becomes independent
of the wavelength, and increases with the depth and steepness of the radial profile of the Alfvén speed.
Authors: Nakariakov, V.M., Hornsey, C., Melnikov, V.F.
Projects: None
|
Publication Status: accepted
Last Modified: 2012-10-30 19:45
|
 
 
 
 
|
|