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Astron. Astrophys. 317, 752-760 (1997)


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Ducted fast waves in coronal loops: curvature effects

J.M. Smith 1, B. Roberts 1 and R. Oliver 2

1 School of Mathematical and Computational Sciences, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, Scotland.
2 Departament de Física, Universitat de les Illes Balears, E-07071 Palma de Mallorca, Spain

Received 23 April 1996 / Accepted 11 June 1996

Abstract

We examine the effect of curvature on fast magnetoacoustic waves in dense coronal loops situated in a potential coronal arcade. The wave equation governing the velocity perturbations has been solved numerically under the zero- [FORMULA] approximation and in the absence of gravity. Due to the curvature of the structure, leaky waves arise. The extent of the leakage depends upon the length, width and density enhancement of the loop, as well as the frequency of oscillation and its geometrical nature. The sausage mode is more affected by curvature and is more leaky than the kink mode. An increase in length, width or gas density ratio reduces the leakage, whilst higher frequencies result in greater energy leakage. Odd modes of oscillation (zero velocity at the loop summit) are more strongly confined than even modes. Modes of oscillation may be destroyed by curvature and above a critical frequency ducted waves cease to exist.

Key words: MHD – Sun: corona – Sun: magnetic field – Sun: oscillations

Send offprint requests to: J.M. Smith

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998

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