Context. The height structure of 3-min oscillations over sunspots is studied in the context of the recently discovered effect of height inversion: over the umbra, the spatial location of the maximum of chromospheric 3-min oscillation power corresponds to the relative decrease in the power of photospheric oscillations. Aims. We investigate whether the height inversion of the power of 3-min oscillations is a common feature of the spatial structure of the oscillations for the majority of sunspots.Methods. Spectrogram sequences of Hα 6563 Å and Fe i 6569 Å over sunspots, acquired with very high cadency (about 2 s or better) are obtained. The distribution of the oscillation power of the line-of-sight velocity signal is studied by using methods of wavelet frequency filtration and Fourier analysis.Results. The effect of the height inversion is found in 9 of 11 analyzed active regions. The interpretation of this effect is possibly connected to both the decrease in the level of photosphere in sunspot umbrae and the magnetic field topology.

The nature of the three-minute and five-minute oscillations observed in sunspots is considered to be an effect of propagation of magnetohydrodynamic (MHD) waves from the photosphere to the solar corona. However, the real modes of these waves and the nature of the filters that result in rather narrow frequency bands of these modes are still far from being generally accepted in spite of a large amount of observational material obtained in a wide range of wave bands of observations. The significance of this field of research is based on the hope that local seismology can be used to find the structure of the solar atmosphere in magnetic tubes of sunspots. We expect that substantial progress can be achieved by simultaneous observations of the sunspot oscillations in different layers of the solar atmosphere in order to gain information on propagating waves. In this study we used a new method that combines the results of an oscillation study made in optical and radio observations. The optical spectral measurements in photospheric and chromospheric lines of the line-of-sight velocity were carried out at the Sayan Solar Observatory. The radio maps of the Sun were obtained with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated with the sunspots were analyzed to study the oscillation processes in the chromospherecorona transition region in the layer with magnetic field B = 2000 G. A high level of instability of the oscillations in the optical and radio data was found. We used a wavelet analysis for the spectra. The best similarities of the spectra of oscillations obtained by the two methods were detected in the three-minute oscillations inside the sunspot umbra for the dates when the active regions were situated near the center of the solar disk. A comparison of the wavelet spectra for optical and radio observations showed a time delay of about 50 seconds of the radio results with respect to optical ones. This implies a MHD wave traveling upward inside the umbral magnetic tube of the sunspot. For the five-minute oscillations the similarity in spectral details could be found only for optical oscillations at the chromospheric level in the umbra region or very close to it. The time delays seem to be similar. Besides three-minute and five-minute ones, oscillations with longer periods (8 and 15 minutes) were detected in optical and radio records. Their nature still requires further observational and theoretical study though for even a preliminary discussion.

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We present an investigation of line-of-sight (LOS) velocity oscillations in solar faculae and sunspots. To study the phase relations between chromospheric and photospheric oscillations of the LOS velocity, we measured the time lag of the chromospheric signal relative to the photospheric one for several faculae and sunspots in a set of spectral line pairs. The measured time lags are different for different objects. The mean measured delay between the oscillations in the five-minute band in faculae is 50 s for the Si i 10 827Å -He i 10 830Å pair; for the pair Fe i 6569Å -Hα 6563Å the mean delay is 20 s; for the pair Fe i 4551Å -Ba ii 4554Å the mean delay is 7 s; for the pair Si i 8536Å -Ca ii 8542Å the mean delay is 20 s. For the oscillations in the three-minute band in sunspot umbrae the mean delay is 55 s for the Si i 10 827Å -He i 10 830Å pair; for the Fe i 6569Å -Hα 6563Å pair it was not possible to determine the delay; for the Fe i 4551Å -Ba ii 4554Å pair the mean delay is 6 s; for the Si i 8536Å -Ca ii 8542Å pair the mean delay is 21 s. Measured delays correspond to the wave propagation speed which significantly exceeds the generally adopted speed of sound in the photosphere. This raises the question of the origin of these oscillations. The possibility that we deal with slow MHD waves is not ruled out.

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