Properties of Sequential Chromospheric Brightenings and Associated Flare Ribbons

TL;DR

This study analyzes the physical properties of sequential chromospheric brightenings (SCBs) during solar flares, revealing their distinct characteristics and proposing a new model for their origin based on high-resolution imaging data.

Contribution

The paper introduces automated methods to identify and analyze SCBs, demonstrating their differences from flare kernels and proposing a heuristic model for their physical origin.

Findings

SCBs differ from flare kernels in intensity, Doppler shifts, duration, and location.

Flare kernels propagate at mean speeds of 0.2 km/s, up to 2.3 km/s.

SCBs precede flare peaks by ~12 minutes and propagate laterally at 41-89 km/s.

Abstract

We report on the physical properties of solar sequential chromospheric brightenings (SCBs) observed in conjunction with moderate-sized chromospheric flares with associated CMEs. To characterize these ephemeral events, we developed automated procedures to identify and track subsections (kernels) of solar flares and associated SCBs using high resolution H-alpha images. Following the algorithmic identification and a statistical analysis, we compare and find the following: SCBs are distinctly different from flare kernels in their temporal characteristics of intensity, Doppler structure, duration, and location properties. We demonstrate that flare ribbons are themselves made up of subsections exhibiting differing characteristics. Flare kernels are measured to have a mean propagation speed of 0.2 km/s and a maximum speed of 2.3 km/s over a mean distance of 5 x 10^3 km. Within the studied population of SCBs, different classes of characteristics are observed with coincident negative, positive, or both negative and positive Doppler shifts of a few km/s. The appearance of SCBs precede peak flare intensity by ~12 minutes and decay ~1 hour later. They are also found to propagate laterally away from flare center in clusters at 41 km/s or 89 km/s. Given SCBs distinctive nature compared to flares, we suggest a different physical mechanism relating to their origin than the associated flare. We present a heuristic model of the origin of SCBs.