The Physical Nature of Spiral Wave Patterns in Sunspots

Abstract

Recently, spiral wave patterns (SWPs) have been detected in 3 minute oscillations of sunspot umbrae, but the nature of this phenomenon has remained elusive. We present a theoretical model that interprets the observed SWPs as the superposition of two different azimuthal modes of slow magnetoacoustic waves driven below the surface in an untwisted and non-rotating magnetic cylinder. We apply this model to SWPs of the line-of-sight (LOS) velocity in a pore observed by the Fast Imaging Solar Spectrograph installed at the 1.6 m Goode Solar Telescope. One- and two-armed SWPs were identified in instantaneous amplitudes of LOS Doppler velocity maps of 3 minute oscillations. The associated oscillation periods are about 160 s, and the durations are about 5 minutes. In our theoretical model, the observed spiral structures are explained by the superposition of non-zero azimuthal modes driven 1600 km below the photosphere in the pore. The one-armed SWP is produced by the slow-body sausage (m = 0) and kink (m = 1) modes, and the two-armed SWP is formed by the slow-body sausage (m = 0) and fluting (m = 2) modes of the magnetic flux tube forming the pore.

arXiv comment10 pages, 5 figures, Published for publication in The Astrophysical Journal Letters

References in corpus (12)

• Spectropolarimetric investigation of the propagation of magnetoacoustic waves and shock formation in sunspot atmospheres
• Relationship between wave processes in sunspots and quasi-periodic pulsations in active region flares
• High-resolution Observations of the Shock Wave Behavior for Sunspot Oscillations with the Interface Region Imaging Spectrograph
• The Nature of Running Penumbral Waves Revealed
• An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers
• Wave dynamics in a sunspot umbra
• Signatures of running penumbral waves in sunspot photospheres
• Detection of Fast-Moving Waves Propagating Outward along Sunspots' Radial Direction in the Photosphere
• Spiral-shaped wavefronts in a sunspot umbra
• Dependence of sunspot photospheric waves on the depth of the source of solar $p-$modes
• Analysis of Helioseismic Power-Spectrum Diagram of A Sunspot
• Origin of Deep Acoustic Sources Associated with Solar Magnetic Structures

Cited by in corpus (12)

• MHD Waves in open coronal structures
• Waves in the lower solar atmosphere: the dawn of next-generation solar telescopes
• Shock Heating Energy of Umbral Flashes Measured with Integral Field Unit Spectroscopy
• Magnetohydrodynamic wave mode identification in circular and elliptical sunspot umbrae: evidence for high order modes
• Source Depth of Three-minute Umbral Oscillations
• Spatial Distribution of Origin of Umbral Waves in a Sunspot Umbra
• Damping of slow surface kink modes in solar photospheric waveguides modeled by one-dimensional inhomogeneities
• The dynamics of 3-minute wavefronts and their relation to sunspot magnetic fields
• Magneto-Acoustic Waves in Magnetic Twisted Flux Tube
• Investigation of the subsurface structure of a sunspot based on the spatial distribution of oscillation centers inferred from umbral flashes
• Origin of the Chromospheric Umbral Waves in Sunspots
• Multi-height Identification of Sausage and Fluting Eigenmodes in a Solar Pore