Multilevel Analysis of Oscillation Motions in Active Regions of the Sun

Abstract

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.

Oscillations above sunspots from the temperature minimum to the corona

“…The 3 min oscillations detected in the microwave range were found to replicate those recorded in the chromosphere of sunspots with a 50-s delay (Abramov-Maximov et al 2011). This implies that the waves propagate from the chromosphere of an umbra to the upper levels.…”

Wave heating of the solar atmosphere

“…The relationship between wave signatures at different heights of the solar atmosphere is reported in many studies (see e.g., O'Shea et al, 2002;Brynildsen et al, 2003;Marsh & Walsh, 2006). They provide information about the phase speed of propagating waves from the time delay of signatures detected at different heights in the solar atmosphere (Abramov-Maximov et al, 2011). The high spatial and temporal resolution of SDO/AIA is enabling additional analyses of the spatial distribution of the frequency, time series analyses, and correlations between the signals at different atmospheric heights (Reznikova et al, 2012;Freij et al, 2014).…”

Long quasi-periodic oscillations of sunspots and nearby magnetic structures

“…Quasi-periodic oscillations in sunspots with periods of 3-5 min are widely known and have been detected at different atmospheric levels (Thomas et al 1984;Banerjee et al 2002;Balthasar & Collados 2005;Kobanov et al 2006;Tlatov & Riehokainen 2009;Abramov-Maximov et al 2011;Botha et al 2011;Reznikova et al 2012). These oscillations are interpreted as the propagation of acoustic slow or fast magnetohydrodynamic waves excited by turbulence flows in the convective zone (Nakariakov 2007;Bogdan 2000;Bogdan et al 2003;Parchevsky & Kosovichev 2009;Felipe et al 2010;Zhugzhda 2008).…”