The impact of a filament eruption on nearby high-lying cool loops

TL;DR

This study presents spectroscopic observations of high-lying cool Mg II loops above the solar limb, capturing their complex dynamics and the impact of a filament eruption that influences plasma motions and line ratios.

Contribution

First spectroscopic analysis of high-lying Mg II loops during a filament eruption, revealing dynamic responses and changes in spectral line ratios.

Findings

High-lying loops reach over 70 Mm in height.

Filament eruption impacts loops, causing plasma flow changes.

Mg h/k line ratio increases after filament impact.

Abstract

The first spectroscopic observations of cool Mg II loops above the solar limb observed by NASA's Interface Region Imaging Spectrograph ({\it IRIS}; \cite{IRIS}) are presented. During the observation period IRIS is pointed off-limb allowing the observation of high-lying loops, which reach over 70~Mm in height. Low-lying cool loops were observed by the {\it IRIS} slit jaw camera for the entire 4 hour observing window. There is no evidence of a central reversal in the line profiles and the Mg II h/k ratio is approximately 2. The Mg II spectral lines show evidence of complex dynamics in the loops with Doppler velocities reaching $\pm$ 40 km/s. The complex motions seen indicate the presence of multiple threads in the loops and separate blobs. Towards the end of the observing period, a filament eruption occurs that forms the core of a coronal mass ejection. As the filament erupts, it impacts these high-lying loops, temporarily impeding these complex flows, most likely due to compression. This causes the plasma motions in the loops become blue-shifted and then red-shifted. The plasma motions are seen before the loops themselves start to oscillate as they reach equilibrium following the impact. The ratio of the Mg h/k lines also increases following the impact of the filament.