Flare-generated acoustic oscillations in solar and stellar coronal loops

¹ Joule Physics Laboratory and Institute for Materials Research, School of Computing, Science & Engineering, University of Salford, Salford, M5 4WT, UK e-mail: D.Tsiklauri@salford.ac.uk
² Physics Department, University of Warwick, Coventry, CV4 7AL, UK
³ Lockheed Martin, Advanced Technology Center Solar & Astrophysics Laboratory, Dept. L9-41, Bldg. 252 3251 Hanover Street, Palo Alto, CA 94304, USA

Received: 18 February 2004
Accepted: 23 April 2004

Abstract

Long period longitudinal oscillations of a flaring coronal loop are studied numerically. In the recent work of Nakariakov et al. (2004) it has been shown that the time dependence of density and velocity in a flaring loop contain pronounced quasi-harmonic oscillations associated with the 2nd harmonic of a standing slow magnetoacoustic wave. In this work we investigate the physical nature of these oscillations in greater detail, namely, their spectrum (using the periodogram technique) and how heat positioning affects mode excitation. We found that excitation of such oscillations is practically independent of the location of the heat deposition in the loop. Because of the change of the background temperature and density, the phase shift between the density and velocity perturbations is not exactly a quarter of the period; it varies along the loop and is time dependent, especially in the case of one footpoint (asymmetric) heating.