The dynamics of 3-min wavefronts and their relation to sunspot magnetic fields

Abstract

We present a study of wave processes occurring in solar active region NOAA 11131 on 10 December 2010, captured by the Solar Dynamics Observatory in the 1600 Å, 304 Å and 171 Å channels. For spectral analysis, we employed pixelized wavelet filtering together with a developed digital technique based on empirical mode decomposition. We studied the ∼3-minute wave dynamics to obtain relationships with the magnetic structuring of the underlying sunspot. We found that during development of wave trains the motion path occurred along a preferential direction, and that the broadband wavefronts can be represented as a set of separate narrowband oscillation sources. These sources become visible as the waves pass through the umbral inhomogeneities caused by the differing magnetic field inclination angles. We found the spatial and frequency fragmentation of wavefronts, and deduced that the combination of narrowband spherical and linear parts of the wavefronts provide the observed spirality. Maps of the magnetic field inclination angles confirm this assumption. We detect the activation of umbral structures as the increasing of oscillations in the sources along the front ridge. Their temporal dynamics are associated with the occurrence of umbral flashes. Spatial localization of the sources is stable over time and depends on the oscillation period. We propose that these sources are the result of wave paths along the loops extending outwards from the magnetic bundles of the umbra. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

Magneto-Acoustic Waves in Magnetic Twisted Flux Tube

“…We think that the spatial and frequency fragmentation of wavefronts as the combination of narrowband spherical and linear parts of the wavefronts can provide the observed spirality. Study of relationship between wave shapes and maps of the magnetic field inclination angles presented in Sych et al (2020) confirm this assumption.…”

“…With more advanced astronomical instruments put into service, more fine structures of MHD waves on the Sun are detected, e.g. the armedspiral wavefronts in the umbrae of sunspots (e.g., Sych & Nakariakov 2014;Su et al 2016;Sych et al 2020). They are likely created by the superpsition of non-zero azimuthal modes driven 1600 km below the photosphere in the sunpots (Kang et al 2019).…”

“…Kang et al (2019) interpreted the spiral wave patterns (SWPs,Sych & Nakariakov 2014;Su et al 2016;Sych et al 2020) as the azimuthal wave modes (m = 0, 1, 2) propagating in an untwisted uniform magnetic cylinder. In this work, we follow their senario and revisit the issue.…”

High-resolution wave dynamics in the lower solar atmosphere

“…Fully formed sunspots are a visually striking manifestation of concentrated magnetic fields in the Sun’s atmosphere. Through novel filtering techniques, Sych et al [42] examine how wave activity in the most intensely magnetic umbral locations allows the embedded fine structure of the sunspot to be probed with high levels of precision. The authors find that the motion path of visible wave trains occurs along preferential directions depending upon the magnetic field inclination angles present within the umbra.…”

“…The authors find that the motion path of visible wave trains occurs along preferential directions depending upon the magnetic field inclination angles present within the umbra. Sych et al [42] propose that small-scale umbral structuring may be responsible for the creation of ubiquitous umbral flashes, and highlight the important need for next-generation larger-aperture solar telescopes to unequivocally answer this question. In keeping with umbral wave observations, Albidah et al [43] examine a sequence of high-cadence H α images that captured a near circularly symmetric sunspot using the HARDcam instrument on the Dunn Solar Telescope.…”