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arXiv · 1507.04795

Detection of Fast-Moving Waves Propagating Outward along Sunspots' Radial Direction in the Photosphere

Junwei Zhao·Ruizhu Chen·Thomas Hartlep·Alexander G. Kosovichev
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Abstract

Helioseismic and magnetohydrodynamic waves are abundant in and above sunspots. Through cross-correlating oscillation signals in the photosphere observed by the SDO/HMI, we reconstruct how waves propagate away from virtual wave sources located inside a sunspot. In addition to the usual helioseismic wave, a fast-moving wave is detected traveling along the sunspot's radial direction from the umbra to about 15 Mm beyond the sunspot boundary. The wave has a frequency range of 2.5 - 4.0 mHz with a phase velocity of 45.3 km/s, substantially faster than the typical speeds of Alfven and magnetoacoustic waves in the photosphere. The observed phenomenon is consistent with a scenario of that a magnetoacoustic wave is excited at approximately 5 Mm beneath the sunspot, and its wavefront travels to and sweeps across the photosphere with a speed higher than the local magnetoacoustic speed. The fast-moving wave, if truly excited beneath the sunspot's surface, will help open a new window to study the internal structure and dynamics of sunspots.

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Junwei Zhao, Ruizhu Chen, Thomas Hartlep, Alexander G. Kosovichev. 2015-07-16. Detection of Fast-Moving Waves Propagating Outward along Sunspots' Radial Direction in the Photosphere. https://doi.org/10.1088/2041-8205%2F809%2F1%2Fl15

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