Magnetohydrodynamic Seismology of Quiet Solar Active Regions

The ubiquity of recently discovered low-amplitude decayless kink oscillations of plasma loops allows for the seismological probing of the corona on a regular basis. In particular, in contrast to traditionally applied seismology that is based on the large-amplitude decaying kink oscillations excited by flares and eruptions, decayless oscillations can potentially provide the diagnostics necessary for their forecasting. We analyzed decayless kink oscillations in several distinct loops belonging to active region NOAA 12107 on 2010 July 10 during its quiet time period, when it was observed on the west limb in extreme ultraviolet by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The oscillation periods were estimated with the use of the motion magnification technique. The lengths of the oscillating loops were determined within the assumption of its semicircular shape by measuring the position of their footpoints. The density contrast in the loops was estimated from the observed intensity contrast accounting for the unknown spatial scale of the background plasma. The combination of those measurements allows us to determine the distribution of kink and Alfvén speeds in the active region. Thus, we demonstrate the possibility of obtaining seismological information about coronal active regions during the quiet periods of time.