Probing Solar Eruption by Tracking Magnetic Cavities and Filaments

Abstract:

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.