Detection of fast-moving waves propagating outward along sunspots' radial direction in the photosphere

Document Type

Article

Publication Date

8-10-2015

Abstract

Helioseismic and magnetohydrodynamic waves are abundant in and above sunspots. Through cross-correlating oscillation signals in the photosphere observed by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, 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-1, substantially faster than the typical speeds of Alfvén 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. 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 for studying the internal structure and dynamics of sunspots.

Identifier

84939193048 (Scopus)

Publication Title

Astrophysical Journal Letters

External Full Text Location

https://doi.org/10.1088/2041-8205/809/1/L15

e-ISSN

20418213

ISSN

20418205

Issue

1

Volume

809

Grant

NAS5-02139

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