Five-minute Periodicities in the Population of Solar Coronal Brightenings

The population of small-scale brightenings observed across broad regions of the quiet-Sun (QS) corona shows coherent strong periodicities of ≈5 minutes and amplitudes of 20% to 30% of the mean. The periodicity is in the total number of detected brightenings, their creation rate, and their mean lifetime. Atmospheric Imaging Assembly/Solar Dynamics Observatory extreme-ultraviolet data spanning 2 hr shows that the periodicity is significant across broad areas of the QS. The periodicities are strong in the hotter 171 Å (300 s period) and 193 Å (340 s period) channels, but absent from the upper chromospheric 304 Å channel, although periodicities are present in the 304 Å channel in other datasets. The density of brightenings is highest above the photospheric network, with the network concentration becoming increasingly pronounced in the hotter channels. An extended study of 11 QS datasets spanning several years shows that these periodic modulations are common, with most periodicities found in the 4 to 6 minutes range. The time profiles of area and brightness for most brightenings show a gradual, nonimpulsive onset inconsistent with local reconnection, and the brightenings are more likely to appear first in the 171 Å channel, then in the hotter 193 Å channel. This suggests that the most plausible formation mechanism is wave or shock dissipation at or near the transition region, likely connected to spicule activity. This heating is modulated by photospheric p -modes and drives the production of transient brightenings in the QS upper chromosphere, transition region, and low corona.