DETECTION OF FAST-MOVING WAVES PROPAGATING OUTWARD ALONG SUNSPOTS’ RADIAL DIRECTION IN THE PHOTOSPHERE

Journal Article · Mon Aug 10 04:00:00 EDT 2015 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/809/1/L15· OSTI ID:22518908

Zhao, Junwei; Chen, Ruizhu ^[1]; Hartlep, Thomas ^[2]; Kosovichev, Alexander G. ^[3]

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1. W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305-4085 (United States)
2. BAER Institute, NASA Ames Research Center, Moffet Field, CA 94043 (United States)
3. Department of Physics, New Jersey Institute of Technology, Newark, NJ 07102 (United States)

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{sup −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.

• OSTI ID: 22518908
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 809; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ALFVEN WAVES
DETECTION
IMAGES
MAGNETOACOUSTIC WAVES
MHZ RANGE
OSCILLATIONS
PHASE VELOCITY
PHOTOSPHERE
SUN
SUNSPOTS
SURFACES