Multi-wavelength observations of substructures in solar flare ribbons

TL;DR

This study provides observational evidence that solar flare ribbons consist of numerous coherent sub-structures called riblets, which exhibit distinct dynamic behaviors and offer insights into chromospheric responses during flares.

Contribution

The paper introduces the concept of riblets as sub-structures within flare ribbons and characterizes their dynamic evolution using high-resolution solar observations.

Findings

Identification of two riblet categories with different velocity patterns

One riblet with a velocity of 18.04 km/s over 67 seconds

Another riblet with an average acceleration of 0.70 km/s² over 22.8 seconds

Abstract

Solar flare ribbons are features in the lower atmosphere that show enhanced emission intensity, particularly noticeable in H$\alpha$ and EUV images of the transition region and upper chromosphere. In this study, we provide observational evidence that the flare ribbons are composed of a large number of coherent sub-structures that we call \textit{riblets}. Our observations, taken with the Swedish 1-m Solar Telescope / CRisp Imaging Spectro-Polarimeter (SST/CRISP) instrument, focused on an X1.5-class flare that occurred on June 10, 2014. Using data obtained from SST/CRISP, we utilize CRISPEX, an interactive graphical user interface tool, to individually track and analyze the dynamic evolution of these riblets, gaining initial insights into their characteristics. Our investigation reveals the existence of two distinct categories of riblets within the flare ribbons. The first category comprises riblets that evolve perpendicular to the ribbon towards the solar surface at a constant velocity over their lifespan. We present one such riblet with a velocity of 18.04 km/s, persisting for a duration of 67 seconds. The second category includes riblets with varying velocities, indicating a more complex and non-linear evolution pattern. We present one such riblet with an average acceleration of 0.70 km/s$^2$ and a duration of 22.8 seconds. Riblets, with their distinct characteristics, provide an opportunity to study the chromospheric response to a solar flare in a more detailed manner.