Observations of Running Penumbral Waves emerging in a Sunspot

Abstract

We present results from the investigation of 5-min umbral oscillations in a single-polarity sunspot of active region NOAA 12132. The spectra of TiO, H$\alpha$, and 304 Å are used for corresponding atmospheric heights from the photosphere to lower corona. Power spectrum analysis at the formation height of H$\alpha$ - 0.6 Å to H$\alpha$ center resulted in the detection of 5-min oscillation signals in intensity interpreted as running waves outside the umbral center, mostly with vertical magnetic field inclination $>15°$. A phase-speed filter is used to extract the running wave signals with speed $v_{ph}>4$ km s${}^{-1}$, from the time series of H$\alpha$ - 0.4 Å images, and found twenty-four 3-min umbral oscillatory events in a duration of one hour. Interestingly, the initial emergence of the 3-min umbral oscillatory events are noticed closer to or at umbral boundaries. These 3-min umbral oscillatory events are observed for the first time as propagating from a fraction of preceding Running Penumbral Waves (RPWs). These fractional wavefronts rapidly separates from RPWs and move towards umbral center, wherein they expand radially outwards suggesting the beginning of a new umbral oscillatory event. We found that most of these umbral oscillatory events develop further into RPWs. We speculate that the waveguides of running waves are twisted in spiral structures and hence the wavefronts are first seen at high latitudes of umbral boundaries and later at lower latitudes of the umbral center.

arXiv comment13 pages, 13 figures, Accepted for publication in The Astrophysical Journal

References in corpus (8)

• Spectropolarimetric investigation of the propagation of magnetoacoustic waves and shock formation in sunspot atmospheres
• Channeling 5-min photospheric oscillations into the solar outer atmosphere through small-scale vertical magnetic flux tubes
• The Nature of Running Penumbral Waves Revealed
• The Influence of the Magnetic Field on Running Penumbral Waves in the Solar Chromosphere
• Propagating slow magnetoacoustic waves in coronal loops observed by Hinode/EIS
• The detection of upwardly propagating waves channelling energy from the chromosphere to the low corona
• Evidence for convection in Sunspot penumbrae
• Analysis of Helioseismic Power-Spectrum Diagram of A Sunspot

Cited by in corpus (5)

• Waves in the lower solar atmosphere: the dawn of next-generation solar telescopes
• Temporal Evolution of the Inverse Evershed Flow
• Spatial Distribution of Origin of Umbral Waves in a Sunspot Umbra
• The dynamics of 3-minute wavefronts and their relation to sunspot magnetic fields
• Origin of the Chromospheric Umbral Waves in Sunspots