Properties of Local Oscillations in the Lower Sunspot Atmosphere

Abstract

Abstract We present a study of wave processes in the sunspot region NOAA 12670 on 2017 August 10 observed by the Goode Solar Telescope in the TiO 7057 Å and Hα 6563 Å spectral lines. To study the distribution of power oscillations and their dynamics, we applied the pixelized wavelet filtering technique. For the first time, we obtained the spatial structure of oscillation sources as the footpoints of fine magnetic tubes, anchored in the sunspot umbra. We found that at the chromosphere level, the variation of emission is a combination of numerous independent oscillations located in the sources with small angular size. Their spatial shape varies from dots and cells in the umbra to filaments in the penumbra. Each narrow spectral harmonic corresponds to its source, without global correlation among themselves. There is a weak background as low-frequency oscillations distributed over the whole umbra. At the photosphere level we found regions with co-phased broadband oscillations of the whole umbra. Their spectrum includes the ∼3 minutes harmonic, whose maximal value is localized in umbral dots, and the low-frequency part near a period of ∼5 minutes. It is shown that the oscillation sources are displaced at different heights with increasing angular size. We assume that the observed spatial distribution of wave sources indicates the existence of a slow subphotospheric resonator with a vertical magnetic field in the umbra and a wave cutoff frequency due to inclination of the magnetic field line in the penumbra.