Large-Amplitude Longitudinal Oscillations Triggered by the Merging of Two Solar Filaments: Observations and Magnetic Field Analysis

TL;DR

This study investigates large-amplitude longitudinal oscillations triggered by the merging of two solar filaments, combining multi-wavelength observations with magnetic field modeling to understand the oscillation dynamics and magnetic structure.

Contribution

It provides the first detailed analysis of filament merging-induced oscillations, combining observational data with magnetic field reconstruction and seismological techniques.

Findings

Oscillation periods are about one hour and decrease over time.

Velocity of plasma oscillations reaches approximately 100 km/s, the largest recorded.

Magnetic field strengths are estimated between 7 and 30 gauss, consistent with reconstructions.

Abstract

We follow the eruption of two related intermediate filaments observed in H$\alpha$ (from GONG) and in EUV (from SDO/AIA) and the resulting large-amplitude longitudinal oscillations of the plasma in the filament channels. The events occurred in and around the decayed active region AR12486 on 2016 January 26. Our detailed study of the oscillation reveals that the periods of the oscillations are about one hour. In H$\alpha$ the period decreases with time and exhibits strong damping. The analysis of 171~\AA\ images shows that the oscillation has two phases, an initial long period phase and a subsequent oscillation with a shorter period. In this wavelength the damping appears weaker than in H$\alpha$. The velocity is the largest ever detected in a prominence oscillation, approximately 100 $\mathrm{\, km \, s^{-1}}$. Using SDO/HMI magnetograms we reconstruct the magnetic field of the filaments modeled as flux ropes by using a flux-rope insertion method. Applying seismological techniques we determine that the radii of curvature of the field lines in which cool plasma is condensed are in the range 75-120~Mm, in agreement with the reconstructed field. In addition, we infer a field strength of $\ge7$ to 30 gauss, depending on the electron density assumed; that is also in agreement with the values from the reconstruction (8-20 gauss). The poloidal flux is zero and the axis flux is of the order of 10$^{20}$ to 10$^{21}$ Mx, confirming the high shear existing even in a non-active filament.