Authors: Marcel Corchado Albelo (University of Colorado, Boulder / National Solar Observatory), Maria Kazachenko (University of Colorado, Boulder / National Solar Observatory), Ryan French (Laboratory for Atmospheric and Space Physics), Vadim Uritsky (CUA at NASA/GSFC) Emily Mason (Predictive Science Inc.) Benjamin Lynch (University of California, Los Angeles.)

In solar flares, magnetic reconnection is understood to be the primary process through which non-potential energy stored in the solar corona is transferred into particle acceleration, bulk plasma motion, and plasma heating. In this study, we use high-resolution flare ribbon observations of an M6.5 class solar flare on June 22, 2015, from the Interface Region Imaging Spectrograph (IRIS) Å Slit-Jaw Imager (SJI), to verify the diagnostic potential of substructure development along the brightest region of the ribbons. From recent theoretical work, the formation of ribbon substructure is linked to the formation of current sheet magnetic structures, which can control the reconnection process dynamics. To track the substructures, we develop a new ribbon tracking algorithm to extract the ribbon’s leading bright front and characterize it using the Correlation Dimension Mapping (CDM) to study both local spatial changes in flare ribbon morphology, and the global temporal evolution of the flare ribbon’s substructures. Our results show that the flare ribbon substructure complexity increases when the magnetic reconnection rates and hard X-ray emission is the highest. Additionally, we find a strong correlation between the line-of-sight turbulent velocity component diagnosed from Si IV IRIS line and the morphological changes of the flare ribbon substructure. These results suggest that the flare ribbon substructure serves as a diagnostic of the development of spatial complexity within the reconnection sheet plasma which is also correlated to the mechanism controlling reconnection dynamics and particle acceleration.