The Effect of Mass Flow on Slow MHD Oscillations of Curved Solar Coronal Loops

Abstract

Slow-mode standing waves are examined in the model of a bent magnetic slab with a plasma flow directed along curved magnetic field lines. The dispersion relation is obtained and studied both numerically and analytically regarding the principal slow mode. It is found that flow decreases the longitudinal oscillating motions and increases the radial kink-like motions, both produced by the principal slow mode. This feature may result in the development of Kelvin-Helmholtz instability when the flow speed exceeds the critical value, and this threshold depends on the azimuthal number \(m\). When flow exists, a quasi-stationary wave structure that satisfies the footpoint boundary conditions has the form of a propagating wave modulated by a sinusoidal envelope. The corresponding eigenfrequencies of oscillations are found to decrease with increasing flow speed until \(u< c_{Ti}\). The results obtained are used for seismological estimation of a plasma flow speed in coronal fan loops experiencing slow mode oscillations.