The effects of magnetic-field geometry on longitudinal oscillations of solar prominences

TL;DR

This study models how the magnetic field geometry of solar prominences affects their large-amplitude longitudinal oscillations, revealing gravity as the main restoring force and the importance of magnetic dip curvature.

Contribution

It provides a full wave analysis of prominence oscillations, deriving a simple frequency expression and highlighting the role of magnetic dip curvature in driving oscillations.

Findings

Gravity is the main restoring force for observed oscillations.

Oscillation frequencies are nearly independent of hot region geometry.

Magnetic dip curvature significantly influences oscillation behavior.

Abstract

We investigate the influence of the geometry of the solar filament magnetic structure on the large-amplitude longitudinal oscillations. A representative filament flux tube is modeled as composed of a cool thread centered in a dipped part with hot coronal regions on either side. We have found the normal modes of the system, and establish that the observed longitudinal oscillations are well described with the fundamental mode. For small and intermediate curvature radii and moderate to large density contrast between the prominence and the corona, the main restoring force is the solar gravity. In this full wave description of the oscillation a simple expression for the oscillation frequencies is derived in which the pressure-driven term introduces a small correction. We have also found that the normal modes are almost independent of the geometry of the hot regions of the tube. We conclude that observed large-amplitude longitudinal oscillations are driven by the projected gravity along the flux tubes, and are strongly influenced by the curvature of the dips of the magnetic field in which the threads reside.