Wave dynamics in a sunspot umbra

Abstract

The high spatial and time resolution data obtained with SDO/AIA for the sunspot in active region NOAA 11131 on 08 December 2010 were analysed with the time-distance plot technique and the pixelised wavelet filtering method. Oscillations in the 3 min band dominate in the umbra. The integrated spectrum of umbral oscillations contains distinct narrowband peaks at 1.9 min, 2.3 min, and 2.8 min. The power significantly varies in time, forming distinct oscillation trains. The oscillation power distribution over the sunspot in the horizontal plane reveals that the enhancements of the oscillation amplitude, or wave fronts, have a distinct structure consisting of an evolving two-armed spiral and a stationary circular patch at the spiral origin, situated near the umbra centre. This structure is seen from the temperature minimum to the corona. In time, the spiral rotates anti-clockwise. The wave front spirality is most pronounced during the maximum amplitude phases of the oscillations. In the low-amplitude phases the spiral breaks into arc-shaped patches. The 2D cross-correlation function shows that the oscillations at higher atmospheric levels occur later than at lower layers. The phase speed is estimated to be about 100 km/s. The fine spectral analysis shows that the central patch corresponds to the high-frequency oscillations, while the spiral arms highlight the lower-frequency oscillations in the 3-min band. The vertical and horizontal radial structure of the oscillations is consistent with the model that interprets umbral oscillations as slow magnetoacoustic waves filtered by the atmospheric temperature non-uniformity in the presence of the magnetic field inclination from the vertical. The mechanism for the polar-angle structure of the oscillations, in particular the spirality of the wave fronts, needs to be revealed.

8 pages, 9 figures, Astronomy and Astrophysics, 2014

References in corpus (10)

• MHD Waves and Coronal Seismology: an overview of recent results
• Relationship between wave processes in sunspots and quasi-periodic pulsations in active region flares
• The Source of Three-minute Magneto-acoustic Oscillations in Coronal Fans
• Three-minute oscillations above sunspot umbra observed with SDO/AIA and NoRH
• Multi-height observations of magnetoacoustic cut-off frequency in a sunspot atmosphere
• Frequency drifts of 3-min oscillations in microwave and EUV emission above sunspots
• Oscillations above sunspots from the temperature minimum to the corona
• Height distribution of the power of 3-min oscillations over sunspots
• Web-Based Data Processing System for Automated Detection of Oscillations with Applications to the Solar Atmosphere
• Multilevel Analysis of Oscillation Motions in Active Regions of the Sun

Cited by in corpus (25)

• Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun
• MHD Waves in open coronal structures
• An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers
• Surge-like oscillations above sunspot light bridges driven by magnetoacoustic shocks
• Sunspot waves and flare energy release
• The Physical Nature of Spiral Wave Patterns in Sunspots
• Local sunspot oscillations and umbral dots
• High-frequency Oscillations in the Atmosphere above a Sunspot Umbra
• Spiral-shaped wavefronts in a sunspot umbra
• A study of sunspot 3 minute oscillations using ALMA and GST
• Evolution Of Super-Sonic Downflows In A Sunspot
• Properties of local oscillations in the lower sunspot atmosphere
• Source Depth of Three-minute Umbral Oscillations
• MHD waves in sunspots
• Peculiarity of the oscillation stratification in sunspot penumbrae
• Fine wave dynamics in umbral flash sources
• The dynamics of 3-minute wavefronts and their relation to sunspot magnetic fields
• Phase speed and frequency-dependent damping of longitudinal intensity oscillations in coronal loop structures observed with AIA/SDO
• Superoscillations in solar MHD waves and their possible role in heating coronal loops
• Very long-periodic pulsations detected simultaneously in a white-light flare and sunspot penumbra
• Magneto-Acoustic Waves in Magnetic Twisted Flux Tube
• Investigation of the subsurface structure of a sunspot based on the spatial distribution of oscillation centers inferred from umbral flashes
• Solar slow magneto-acoustic-gravity waves: an erratum correction and a revisited scenario
• Behaviour of oscillations in loop structures above active regions
• Origin of the Chromospheric Umbral Waves in Sunspots