The Physical Nature of Spiral Wave Patterns in Sunspots

Kang, Jin Wook; Chae, Jongchul; Nakariakov, V. M.; Cho, Kyuhyoun; Kwak, Hannah; Lee, Kyeo-Re

doi:10.3847/2041-8213/ab1f6c

Cited by 26 publications

(35 citation statements)

References 38 publications

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“…Recent observations (Chae et al 2017;Cho et al 2019;Kang et al 2019) rather support the notion that the sources of excitation are located below the atmosphere, as has commonly been modeled by the piston motion at the bottom of the atmosphere in previous theoretical studies (e.g., Fleck & Schmitz 1991;Kalkofen et al 1994;Sutmann & Ulmschneider 1995). These studies found that regardless of the specific form of the piston driving, the oscillations with a frequency close to the cutoff prevail in high altitudes of the atmosphere.…”

Section: Introductionmentioning

confidence: 73%

Linear Acoustic Waves in a Nonisothermal Atmosphere. II. Photospheric Resonator Model of Three-minute Umbral Oscillations

Chae

Kang

Litvinenko

2019

ApJ

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The velocity oscillations observed in the chromosphere of sunspot umbrae resemble a resonance in that their power spectra are sharply peaked around a period of about three minutes. In order to describe the resonance that leads to the observed 3-minute oscillations, we propose the photospheric resonator model of acoustic waves in the solar atmosphere. The acoustic waves are driven by the motion of a piston at the lower boundary, and propagate in a nonisothermal atmosphere that consists of the lower layer (photosphere), where temperature rapidly decreases with height, and the upper layer (chromosphere), where temperature slowly increases with height. We have obtained the following results: (1) The lower layer (photosphere) acts as a leaky resonator of acoustic waves. The bottom end is established by the piston, and the top end by the reflection at the interface between the two layers. (2) The temperature minimum region partially reflects and partially transmits acoustic waves of frequencies around the acoustic cutoff frequency at the temperature minimum. (3) The resonance occurs in the photospheric layer at one frequency around this cutoff frequency. (4) The waves escaping the photospheric layer appear as upwardpropagating waves in the chromosphere. The power spectrum of the velocity oscillation observed in the chromosphere can be fairly well reproduced by this model. The photospheric resonator model was compared with the chromospheric resonator model and the propagating wave model.

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Section: Introductionmentioning

confidence: 73%

Linear Acoustic Waves in a Nonisothermal Atmosphere. II. Photospheric Resonator Model of Three-minute Umbral Oscillations

Chae

Kang

Litvinenko

2019

ApJ

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“…The same can be said for waves in chromospheres above sunspot umbrae. For instance, the long-known spiral wave patterns (SWPs) with periodicities of ∼ 3 mins (e.g., Su et al 2016, and references therein) were recently shown to be compatible with the superposition of slow body modes with m = 0 and m = 1 (m = 0 and m = 2) in the case of one-armed (two-armed) SWPs (Kang et al 2019). Likewise, clear signatures of slow kink body modes were identified in the temporally and spatially filtered H α image sequences acquired with ROSA mounted on the Dunn Solar Telescope (DST, Jess et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Damping of Slow Surface Kink Modes in Solar Photospheric Waveguides Modeled by One-dimensional Inhomogeneities

Chen

Doorsselaere

et al. 2021

ApJ

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Given the recent interest in magnetohydrodynamic (MHD) waves in pores and sunspot umbrae, we examine the damping of slow surface kink modes (SSKMs) by modeling solar photospheric waveguides with a cylindrical inhomogeneity comprising a uniform interior, a uniform exterior, and a continuous transition layer (TL) in between. Performing an eigen-mode analysis in linear, resistive, gravity-free MHD, our approach is idealized in that, among other things, our equilibrium is structured only in the radial direction. We can nonetheless address two damping mechanisms simultaneously, one being the Ohmic resistivity, and the other being the resonant absorption of SSKMs in the cusp and Alfvén continua. We find that the relative importance of the two mechanisms depends sensitively on the magnetic Reynolds number (R m ). Resonant absorption is the sole damping mechanism for realistically large values of R m , and the cusp resonance in general dominates the Alfvén one unless the axial wavenumbers are at the lower end of the observationally relevant range. We also find that the thin-boundary approximation holds only when the TL-width-to-radius ratios are much smaller than nominally expected. The Ohmic resistivity is far more important for realistically small R m . Even in this case, SSKMs are only marginally damped, with damping-time-to-period-ratios reaching ∼ 10 in the parameter range we examine.

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“…It has been assumed that the waveguides of running waves are twisted into local spiral structures [14]. A model for the appearance of spiral wavefronts was proposed in relation to their propagation in radial magnetic fields [15]. The authors concluded that rotating structures can occur in a superposition of non-zero- m azimuthal slow modes.…”

Section: Introductionmentioning

confidence: 99%

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

Сыч

Jess

2020

Phil. Trans. R. Soc. A.

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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’.

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The Physical Nature of Spiral Wave Patterns in Sunspots

Cited by 26 publications

References 38 publications

Linear Acoustic Waves in a Nonisothermal Atmosphere. II. Photospheric Resonator Model of Three-minute Umbral Oscillations

Linear Acoustic Waves in a Nonisothermal Atmosphere. II. Photospheric Resonator Model of Three-minute Umbral Oscillations

Damping of Slow Surface Kink Modes in Solar Photospheric Waveguides Modeled by One-dimensional Inhomogeneities

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

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