Observations of oppositely directed umbral wavefronts rotating in sunspots obtained from the new solar telescope of BBSO

Journal Article · Mon Feb 01 00:00:00 EST 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/817/2/117· OSTI ID:22887105

Su, J. T.; Priya, T. G.; Bai, X. Y.; Chen, J.; Zhang, M. ^[1]; Ji, K. F. ^[2]; Cao, W. ^[3]; Banerjee, D. ^[4]; Zhao, J. S. ^[5]

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1. Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)
2. Kunming University of Science and Technology, Kunming 650093 (China)
3. Big Bear Solar Observatory, 40386 North Shore Lane, Big Bear City, CA 92314 (United States)
4. Indian Institute of Astrophysics, Koramangala, Bangalore 560034 (India)
5. Key Laboratory of Planetary Sciences, Purple Mountain Observatory, CAS, Nanjing 210008 (China)

We study the umbral waves as observed by chromospheric imaging observations of two sunspots with the New Solar Telescope at the Big Bear Solar Observatory. We find that the wavefronts (WFs) rotate clockwise and form a one-armed spiral structure in the first sunspot, whereas two- and three-armed structures arise in the second sunspot where the WFs rotate anticlockwise and clockwise alternately. All the spiral arms display propagation outwards and become running penumbral waves once they cross the umbral boundaries, suggesting that the umbral and penumbral waves propagate along the same inclined field lines. We propose that the one-armed spiral structure may be produced by the WF reflections at the chromospheric umbral light bridge, and the multi-armed spirals may be related to the twist of the magnetic field in the umbra. Additionally, the time lag of the umbral oscillations in between the data of He i 10830 Å and Hα−0.4 Å is ∼17 s, and it is ∼60 s for that in between the data of 304 Å and Hα−0.4 Å. This indicates that these disturbances are slow magnetoacoustic waves in nature, and that they propagate upward along the inclined lines with fast radial expansions causing horizontal velocities of the running waves.

• OSTI ID: 22887105
• Journal Information: Astrophysical Journal, Vol. 817, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CHROMOSPHERE
DISTURBANCES
MAGNETIC FIELDS
MAGNETOACOUSTIC WAVES
MAGNETOACOUSTICS
OSCILLATIONS
REFLECTION
SUN
SUNSPOTS
TELESCOPES
VELOCITY