Stochastic Transients as a Source of Quasi-Periodic Processes in the Solar Atmosphere

Walsh

2016

ApJ

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Fast magnetoacoustic wave is an important tool for inferring solar atmospheric parameters. We numerically simulate the propagation of fast wave pulses in randomly structured plasmas mimicking the highly inhomogeneous solar corona. A network of secondary waves is formed by a series of partial reflections and transmissions. These secondary waves exhibit quasi-periodicities in both time and space. Since the temporal and spatial periods are related simply through the fast wave speed, we quantify the properties of secondary waves by examining the dependence of the average temporal period (p) on the initial pulse width (w 0 ) as well as the density contrast (δ ρ ) and correlation length (L c ) that characterize the randomness of the equilibrium density profiles. For small-amplitude pulses, δ ρ does not alterp significantly. Large-amplitude pulses, on the other hand, enhance the density contrast when δ ρ is small but have a smoothing effect when δ ρ is sufficiently large. We found thatp scales linearly with L c and that the scaling factor is larger for a narrower pulse. However, in terms of the absolute values ofp, broader pulses generate secondary waves with longer periods, and this effect is stronger in random plasmas with shorter correlation lengths. Secondary waves carry the signatures of both the leading wave pulse and background plasma, our study may find applications in MHD seismology by exploiting the secondary waves detected in the dimming regions after CMEs or EUV waves.

Section: Quasi-periodicity Of Secondary Wavessupporting

confidence: 88%

“…The randomness in spatial structuring is transformed into the randomness in the temporal domain. As demonstrated in Yuan et al (2016), quasi-periodicity is an intrinsic property of a random time series, and the quasi-periods are usually a few times longer than the timescales of the transients.…”

Section: Quasi-periodicity Of Secondary Wavesmentioning

confidence: 99%

Secondary Fast Magnetoacoustic Waves Trapped in Randomly Structured Plasmas

Walsh

2016

ApJ

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“…Recently, several authors have reported that small scale jets and spicules at transition region and chromosphere are associated with with PDs seen in polar plumes and polar coronal holes Jiao et al 2015;Samanta et al 2015;Bryans et al 2016;Yuan et al 2016). Reflections of propagating slow waves were also reported in hot and flaring coronal loops using AIA (Kumar et al 2013(Kumar et al , 2015 and XRT observations (Mandal et al 2016).…”

Section: Introductionmentioning

confidence: 99%

First Imaging Observation of Standing Slow Wave in Coronal Fan Loops

Pant

Tiwari

et al. 2017

ApJL

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We observe intensity oscillations along coronal fan loops associated with the active region AR 11428. The intensity oscillations were triggered by blast waves which were generated due to X-class flares in the distant active region AR 11429. To characterise the nature of oscillations, we created time-distance maps along the fan loops and noted that the intensity oscillations at two ends of the loops were out of phase. As we move along the fan loop, the amplitude of the oscillations first decreased and then increased. The out-of-phase nature together with the amplitude variation along the loop implies that these oscillations are very likely to be standing waves. The period of the oscillations are estimated to be ∼27 min, damping time to be ∼45 min and phase velocity projected in the plane of sky ∼ 65-83 km s −1 . The projected phase speeds were in the range of acoustic speed of coronal plasma at about 0.6 MK which further indicates that these are slow waves. To best of our knowledge, this is the first report on the existence of the standing slow waves in non-flaring fan loops.

“…Waves and oscillations are established within a sunspot, which act as a waveguide in response to the dynamics and turbulence of the solar interior (see a comprehensive review by Khomenko & Collados 2015). Analysis of the spatial and height distributions of the oscillations can reveal the magnetic (Reznikova & Shibasaki 2012;Yuan et al 2014b,a;Jess et al 2013Jess et al , 2016 and thermal structures of a sunspot (Zhugzhda 2008;Botha et al 2011;Snow et al 2015;Yuan et al 2016;Chae & Goode 2015;Kwak et al 2016). An isolated sunspot could be assumed to have an expanding axisymmetric magnetic field; inhomogeneities, such as light bridges, umbral dots, are normally observed at a variety of scales (see a review by Borrero & Ichimoto 2011).…”

Section: Introductionmentioning

confidence: 99%

Abnormal oscillation modes in a waning light bridge

Walsh

2016

A&A

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Context. A sunspot acts as a waveguide in response to the dynamics of the solar interior; the trapped waves and oscillations could reveal its thermal and magnetic structures. Aims. We study the oscillations in a sunspot intruded by a light bridge, and the details of these oscillations could reveal the fine structure of the magnetic topology. Methods. We used the Solar Dynamics Observatory/Atmospheric Imaging Assembly data to analyse the oscillations in the emission intensity of light bridge plasma at different temperatures, and we investigated their spatial distributions. Results. The extreme ultraviolet emission intensity exhibits two persistent oscillations at five-minute and sub-minute ranges. The spatial distribution of the five-minute oscillation follows the spine of the bridge, whereas the sub-minute oscillations overlap with two flanks of the bridge. Moreover, the sub-minute oscillations are highly correlated in spatial domain, however, the oscillations at the eastern and western flanks are asymmetric with regard to the lag time. In the meantime, jet-like activities are only found at the eastern flank. Conclusions. Asymmetries in the form of oscillatory pattern and jet-like activities are found between two flanks of a granular light bridge. Based on our study and recent findings, we propose a new model of twisted magnetic field for a light bridge and its dynamic interactions with the magnetic field of a sunspot.