Qualities of Sequential Chromospheric Brightenings Observed in Optical and UV Images

TL;DR

This study analyzes the physical qualities and temporal behavior of sequential chromospheric brightenings (SCBs) observed in optical and UV images, revealing their spatial constraints and energy budget relative to solar flares.

Contribution

It introduces an automated detection method for SCBs across multiple wavelengths and distinguishes three types of SCBs using Doppler velocities, advancing understanding of their properties.

Findings

SCBs appear earlier and last longer in H-alpha than in AIA measurements.

SCBs are spatially confined to the mid-chromosphere.

Energy of SCBs is less than 0.01% of total flare energy.

Abstract

Chromospheric flare ribbons observed in H-alpha appear well-organized when first examined: ribbons impulsively brighten, morphologically evolve, and exponentially decay back to pre-flare levels. Upon closer inspection of H-alpha flares, there is often a significant number of compact areas brightening in concert with the flare eruption but are spatially separated from the evolving flare ribbon. One class of these brightenings is known as sequential chromospheric brightenings (SCBs). SCBs are often observed in the intimidate vicinity of erupting flares and are associated with coronal mass ejections. In the past decade there have been several previous investigations of SCBs. These studies have exclusively relied upon H-alphaimages to discover and analyze these ephemeral brightenings. This work employs the automated detection algorithm of Kirk et al. (2011) to extract the physical qualities of SCBs in observations of ground-based H-alpha images and complementary AIA images in HeII, Civ, and 1700 \AA. The meta-data produced in this tracking process are then culled using complementary Doppler velocities to isolate three distinguishable types of SCBs. From a statistical analysis, we find that the SCBs at the chromospheric H-alpha layer appear earlier, and last longer than their corresponding signatures measured in AIA. From this multi-layer analysis, we infer that SCBs are spatially constrained to the mid-chromosphere. We also derive an energy budget to explain SCBs in which SCBs have a postulated energy of not more than 0.01% of the total flare energy.