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

Junwei Zhao, Ruizhu Chen, Thomas Hartlep, Alexander G. Kosovichev

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

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.

Original languageEnglish (US)
Article numberL15
JournalAstrophysical Journal Letters
Volume809
Issue number1
DOIs
StatePublished - Aug 10 2015

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Sun: helioseismology
  • Sun: oscillations
  • sunspots

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