The period ratio for kink and sausage modes in a magnetic slab

School of Mathematics and Statistics, University of St. Andrews, St. Andrews, Fife, KY16 9SS, Scotland
e-mail: cicely@mcs.st-andrews.ac.uk, br@st-and.ac.uk

Received: 23 July 2010
Accepted: 23 November 2010

Abstract

Aims. Increasing observational evidence of wave modes in the solar corona brings us to a closer understanding of that medium. Coronal seismology allows us to combine wave observations and theory to determine otherwise unknown parameters. The period ratio, P₁/2P₂, between the period P₁ of the fundamental mode and twice the period P₂ of its first overtone, is one such tool of coronal seismology and its departure from unity provides information about the structure of the corona.

Methods. We consider analytically the period ratio for the fast kink and sausage modes of a magnetic slab, discussing both an Epstein density profile and a simple step function profile.

Results. Transverse density structuring in the form of an Epstein profile or a step function profile may contribute to the shift of the period ratio for long thin slab-like structures.