Spectroscopic observations of evolving flare ribbon substructure suggesting origin in current sheet waves

TL;DR

This study uses high-resolution spectroscopic imaging to analyze flare ribbon substructure, revealing quasi-periodic oscillations likely caused by waves in the coronal current sheet, advancing understanding of flare dynamics.

Contribution

It provides new evidence linking flare ribbon oscillations to waves in the current sheet, such as tearing modes or Kelvin-Helmholtz instabilities.

Findings

Detection of quasi-periodic oscillations in flare ribbons.

Support for wave phenomena in the coronal current sheet as the origin.

Identification of potential wave types like tearing mode or Kelvin-Helmholtz instability.

Abstract

We present imaging and spectroscopic observations from the Interface Region Imaging Spectrograph (IRIS) of the evolution of the flare ribbon in the SOL2014-04-18T13:03 M-class flare event, at high spatial resolution and time cadence. These observations reveal small-scale substructure within the ribbon, which manifests as coherent quasi-periodic oscillations in both position and Doppler velocities. We consider various alternative explanations for these oscillations, including modulation of chromospheric evaporation flows. Among these we find the best support for some form of wave localized to the coronal current sheet, such as a tearing mode or Kelvin-Helmholtz instability.