Magnetohydrodynamic Seismology of Quiet Solar Active Regions

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 Alfvén speeds in the active region. Thus, we demonstrate the possibility to obtain seismological information about coronal active regions during the quiet periods of time.

Kink Oscillations of Coronal Loops

“…Kink oscillations are used for estimating the absolute value of the magnetic field (e.g., Nakariakov and Ofman 2001) and its variation along the loop (Verth and Erdélyi 2008), the spatial scale of the density stratification (e.g., Andries et al 2005), and give information about transverse profiles of the Alfvén speed and mass density (Aschwanden et al 2003), including its steepness (Pascoe et al 2016b). More recently, it was demonstrated that the ubiquitous kink oscillations observed in coronal active regions during the quiet time periods, allow for the seismological mapping of the Alfvén speed and magnetic field (e.g., Anfinogentov and Nakariakov 2019). Kink oscillations in loops of the sigmoid shape have been shown to carry the information about the free magnetic energy associated with non-potential field geometry (e.g., Magyar and Nakariakov 2020).…”

Transverse Loop Oscillations via Vortex Shedding: A Self-oscillating Process

“…Alongside those larger-amplitude decaying oscillations, a second category of low-amplitude, transverse waves occurring in coronal loops has also been observed in recent years. These waves were first detected by Wang et al (2012) and Tian et al (2012), and were proven to be omnipresent in active region coronal loops (Anfinogentov et al 2013(Anfinogentov et al , 2015, making them possible tools for coronal seismology (Anfinogentov & Nakariakov 2019;Yang et al 2020). These decay-less oscillations have a near constant amplitude over the course of many periods, with frequencies equal to that of the fundamental standing kink mode (Nisticò et al 2013), as well as its second harmonic (Duckenfield et al 2018).…”

Motion Magnification in Solar Imaging Data Sequences in the Sub-pixel Regime

“…Similar oscillations are detected as persistent Doppler-shift oscillations at loop apexes (Tian et al, 2012;Li et al, 2018). Anfinogentov, Nisticò, and Nakariakov (2013) demonstrated the ubiquity of decayless kink oscillations of coronal loops, which opens up interesting perspectives for regular seismological probing of the magnetic field in coronal active regions (Anfinogentov and Nakariakov, 2019). Of special interest is the diagnostics of the magnetic-field sigmoidity (Magyar and Nakariakov, 2020), and the related free magnetic energy.…”