Abstract
Abstract We study intensity variations, as measured by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, in a solar coronal arcade using a newly developed analysis procedure that employs spatio-temporal autocorrelations. We test our new procedure by studying large-amplitude oscillations excited by nearby flaring activity within a complex arcade and detect a dominant periodicity of 12.31 minutes. We compute this period in two ways: from the traditional time–distance fitting method and using our new autocorrelation procedure. The two analyses yield consistent results. The autocorrelation procedure is then implemented on time series for which the traditional method would fail due to the complexity of overlapping loops and a poor contrast between the loops and the background. Using this new procedure, we discover the presence of small-amplitude oscillations within the same arcade with 9.13 and 9.81 minute periods prior and subsequent to the large-amplitude oscillations, respectively. Consequently, we identify these as “decayless” oscillations that have only been previously observed in nonflaring loop systems.
Highlights
Solar coronal arcades consist of brightly illuminated arches of hot plasma referred to as coronal loops
We study coronal loop oscillations on the southeastern limb using extreme ultraviolet (EUV) images obtained by Atmospheric Imaging Assembly (AIA)/Solar Dynamics Observatory (SDO) with unprecedented spatial (1 pixel ≈ 0.6′′) and temporal (12 s cadence) resolutions on 2014 January 27
From the sequence of EUV images, it appears that the wavefront propagated away from the limb followed by the first M-class flare
Summary
Solar coronal arcades consist of brightly illuminated arches of hot plasma referred to as coronal loops. Aschwanden et al (2002) investigated 17 events with TRACE data and concluded that most of the oscillating loops do not fit the simple model of kink eigenmode oscillations, but instead suggest that the oscillations are flare-induced impulsively generated MHD waves, which decay rapidly either due to damping or wave leakage. Such observed large-amplitude attenuation has been generally attributed to resonant absorption, a mode conversion process whereby energy is transferred from the global transverse waves to local Alfvénic waves (e.g., Goossens et al 2002; Ruderman & Roberts 2002; Hindman & Jain 2018).
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