Wave dynamics in sunspot atmosphere (Invited)

Abstract:

The temporal, spatial and frequency dynamics of 3-min slow magnetoacoustic wave propagating in sunspot active region NOAA 11131 on December 8, 2010 is analyzed. We used the Pixelised Wavelet Filtering (PWF) method to compute narrowband power maps of SDO/AIA imaging datasets in the 1700A, 1600A, 304A, 171A, 211A, 193A, 131A and 335A bandpasses, that correspond to different heights. For the 1D data preparation we used the method of time-distance plots. It is shown that there are time intervals where the changes of 1D shape of wave fronts was observed. There is correlation between power of 3-min oscillations and shape of waves. In maxima power we observed symmetrical propagation. Oscillation minima connect with the asymmetrical propagation and collapse of the wave fronts. Two-dimensional spectral analysis shows the spatial structure of wave fronts as a spiral with two arms, connected with pulsed source in umbra center. We observed counterclockwise rotation of spiral during the 3-min oscillation cycle with extend arms up to umbra border. Decreasing of power oscillation connect with waves transform from spiral to quasi-spherical shape. We found that helicity is exist on all heights of atmosphere above the sunspot. At different wavelengths there are time delays between upward wave propagation. We use the spatial cross-correlation method between narrowband details in umbra for obtain value of delays. The calculated values for baseline 1700A showed delays: 4.5 sec. for 1600A, 16.8 sec for 304A, 17.9 sec for 45 sec and 193A for 167A. The propagating speed of the waves about 90-100 km/s. The spatial-frequency structure of spiral shown a set of narrowband details in 3-min waveband, spatially distributed in different parts of sunspot umbra. There is a central, high frequency component (~ 9.3mHz) as a pulsing source and low- frequency component (~ 6.4mHz - 4.9mHz) as a expending wave fronts. On coronal level we observed a radial motion along coronal loops. We suppose that observed helicity have projection nature and based on spatial distribution of magnetic waveguides in the sunspot and height of emission generation. We can conclude that the cut-off frequency is a main factor of appearance a narrowband details in a 3-min oscillations waveband and observed helicity in wave propagation.