Magnetohydrodynamic Seismology of Quiet Solar Active Regions

TL;DR

This study demonstrates how decayless kink oscillations in solar coronal loops can be used for seismological diagnostics of active regions during quiet periods, providing insights into the coronal plasma properties.

Contribution

It introduces a method to perform seismology of active regions using decayless oscillations during quiet times, expanding the diagnostic capabilities beyond flare-induced oscillations.

Findings

Determined oscillation periods using motion magnification.

Estimated loop lengths assuming semicircular shape.

Derived kink and Alfvén speeds in the active region.

Abstract

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 which 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 analysed decayless kink oscillations in several distinct loops belonging to active region NOAA 12107 on 10 July 2010 during its quiet time period, when it was observed on the West limb in EUV by the Atmospheric Imaging Assembly on-board 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 foot-points. 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 Alfv\'en speeds in the active region. Thus, we demonstrate the possibility to obtain seismological information about coronal active regions during the quiet periods of time.