Effects of background periodic flow on MHD fast wave propagation to a coronal loop

TL;DR

This study explores how a small, periodic background flow influences MHD fast wave propagation and energy absorption in coronal loops, revealing new flow regimes and resonance behaviors.

Contribution

It introduces a novel analysis of periodic flow effects on wave absorption and overreflection in coronal loops, extending previous constant flow models.

Findings

Periodic flow enhances wave absorption for antiparallel flow.

Giant overreflection occurs in certain flow configurations.

Weak effects observed in other flow regimes.

Abstract

We investigate the propagation of MHD fast waves into a cylindrical coronal loop through an inhomogeneous stationary flow region. The background flow is assumed to have a small, spatially periodic structure in addition to a constant speed. We focus on the absorption of the wave energy in Alfv\'{e}n resonance, comparing with the constant flow case. A new flow (absorption) regime is induced by the periodic flow structure which enhances the absorption for the antiparallel flow and inverse absorption (overreflection) for the parallel flow with respect to the axial wave vector, depending on the transitional layer and flow profiles. A giant overreflection and anomalous absorption behavior arise for some flow configurations. In the other flow regimes, its effect on the absorption is shown to be weak.