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Observations of Running Penumbral Waves Emerging in a Sunspot  

Priya T G   Submitted: 2018-04-03 19:12

We present results from the investigation of 5 minute umbral oscillations in a single-polarity sunspot of activeregion NOAA 12132. The spectra of TiO, Hα, and 304 Å are used for corresponding atmospheric heights from thephotosphere to lower corona. Power spectrum analysis at the formation height of Hα - 0.6 Å to the Hα centerresulted in the detection of 5 minute 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 vph > 4 km s-1 , from the time series of Hα - 0.4 Å images, and found twenty-four 3 minute umbral oscillatory events in a duration of one hour. Interestingly, the initial emergence of the 3 minuteumbral oscillatory events are noticed closer to or at umbral boundaries. These 3 minute umbral oscillatory eventsare observed for the first time as propagating from a fraction of preceding running penumbral waves (RPWs).These fractional wavefronts rapidly separate from RPWs and move toward the umbral center, wherein they expandradially outwards suggesting the beginning of a new umbral oscillatory event. We found that most of these umbraloscillatory events develop further into RPWs. We speculate that the waveguides of running waves are twisted inspiral structures and hence the wavefronts are first seen at high latitudes of umbral boundaries and later at lowerlatitudes of the umbral center.

Authors: T. G. Priya, Cao Wenda, Su Jiangtao, Chen Jie, Mao Xinjie, Deng Yuanyong and Erdélyi Robert
Projects: BBSO/NST

Publication Status: Published in The Astrophysical Journal
Last Modified: 2018-04-04 12:20
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Observations of Running Penumbral Waves Emerging in a Sunspot

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