Signatures of running penumbral waves in sunspot photospheres

Abstract

The highly dynamic atmosphere above sunspots exhibits a wealth of magnetohydrodynamic (MHD) waves. Recent studies suggest a coupled nature of the most prominent phenomena: umbral flashes (UFs) and running penumbral waves (RPWs). From an observational point of view, we perform a height-dependent study of RPWs, compare their wave characteristics and aim to track down these so far only chromospherically observed phenomena to photospheric layers to prove the upward propagating field-guided nature of RPWs. We analyze a time series (58\,min) of multi-wavelength observations of an isolated circular sunspot (NOAA11823) taken at high spatial and temporal resolution in spectroscopic mode with the Interferometric BIdimensional Spectro-polarimeter (IBIS/DST). By means of a multi-layer intensity sampling, velocity comparisons, wavelet power analysis and sectorial studies of time-slices, we retrieve the power distribution, characteristic periodicities and propagation characteristics of sunspot waves at photospheric and chromospheric levels. Signatures of RPWs are found at photospheric layers. Those continuous oscillations occur preferably at periods between 4-6\,min starting at the inner penumbral boundary. The photospheric oscillations all have a slightly delayed, more defined chromospheric counterpart with larger relative velocities (which are linked to preceding UF events). In all layers the power of RPWs follows a filamentary fine-structure and shows a typical ring-shaped power distribution increasing in radius for larger wave periods. The analysis of time-slices reveals apparent horizontal velocities for RPWs at photospheric layers of $\approx 50km/s$ which decrease to $\approx 30km/s$ at chromospheric heights. The observations strongly support the scenario of RPWs being upward propagating slow-mode waves guided by the magnetic field lines.

6 pages, 6 figures

References in corpus (3)

• The Nature of Running Penumbral Waves Revealed
• The Influence of the Magnetic Field on Running Penumbral Waves in the Solar Chromosphere
• Lateral downflows in sunspot penumbral filaments and their temporal evolution

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• Magnetoacoustic Waves in a Stratified Atmosphere with a Magnetic Null Point
• The Physical Nature of Spiral Wave Patterns in Sunspots
• Inversions of synthetic umbral flashes: effects of the scanning time on the inferred atmospheres
• High-frequency Oscillations in the Atmosphere above a Sunspot Umbra
• Accurately constraining velocity information from spectral imaging observations using machine learning techniques
• Source Depth of Three-minute Umbral Oscillations
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• Spatial Distribution of Origin of Umbral Waves in a Sunspot Umbra
• Magnetic field reconstruction based on sunspot oscillations
• Peculiarity of the oscillation stratification in sunspot penumbrae
• Magnetic field fluctuations in the shocked umbral chromosphere
• The role of the Lorentz force in sunspot equilibrium