Probing Solar Eruption by Tracking Magnetic Cavities and Filaments

A solar eruption is a tremendous explosion on the Sun that happens when energy stored in twisted (or distorted) magnetic fields is suddenly released. When this field is viewed along the axis of the twist in projection at the limb, e.g. in EUV or white-light coronal images, the outer portions of the pre-eruption magnetic structure sometimes appears as a region of weaker emission, called a "coronal cavity," surrounded by a brighter envelope. Often a chromospheric filament resides near the base of the cavity and parallel to the cavity's central axis. Typically, both the cavity and filament move outward from the Sun at the start of an eruption of the magnetic field in which the cavity and filament reside. Studying properties the cavities and filaments just prior to and during eruption can help constrain models that attempt to explain why and how the eruptions occur. In this study, we examined six different at-limb solar eruptions using images from the Extreme Ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO). For four of these eruptions we observed both cavities and filaments, while for the remaining two eruptions, one had only a cavity and the other only a filament visible in EIT images. All six eruptions were in comparatively-quiet solar regions, with one in the neighborhood of the polar crown. We measured the height and velocities of the cavities and filaments just prior to and during the start of their fast-eruption onsets. Our results support that the filament and cavity are integral parts of a single large-scale erupting magnetic-field system. We examined whether the eruption-onset heights were correlated with the expected magnetic field strengths of the eruption-source regions, but no clear correlation was found. We discuss possible reasons for this lack of correlation, and we also discuss future research directions. The research performed was supported by the National Science Foundation under Grant No. AGS-1460767; J.J. participated in the Research Experience for Undergraduates (REU) program, at NASA/MSFC. Additional support was from a grant from the NASA LWS program.