Automated Detection of Rapid Variability of Moss Using SDO/AIA and Its Connection to the Solar Corona

Abstract

Active region moss—the upper transition region of hot loops—was observed exhibiting rapid intensity variability on timescales of order 15 s by Testa et al. in a short time series (∼150 s) data set from Hi-C (High-resolution Coronal Imager). The intensity fluctuations in the subarcsecond 193A images (∼1.5 MK plasma) were uncharacteristic of steadily heated moss and were considered an indication of heating events connected to the corona. Intriguingly, these brightenings displayed a connection to the ends of transient hot loops seen in the corona. Following the same active region, AR11520, for 6 days, we demonstrate an algorithm designed to detect the same temporal variability in lower resolution Atmospheric Imaging Assembly (AIA) data, significantly expanding the number of events detected. Multiple analogous regions to the Hi-C data are successfully detected, showing moss that appears to “sparkle” prior to clear brightening of connected high-temperature loops; this is confirmed by the hot AIA channels and the isolated Fe  xviii emission. The result is illuminating, as the same behavior has recently been shown by Polito et al. while simulating nanoflares with a beam of electrons depositing their energy in the lower atmosphere. Furthermore, the variability is localized mostly to the hot core of the region, hence we reinforce the diagnostic potential of moss variability as the driver of energy release in the corona. The ubiquitous nature of this phenomenon, and the ability to detect it in data with extended time series, and large fields of view, opens a new window into investigating the coronal heating mechanism.