Long-Term Oscillations of Sunspots from Simultaneous Observations with the Nobeyama Radioheliograph and Solar Dynamics Observatory

Abstract

We present an investigation of oscillatory processes with periods in the range of several tens of minutes for some single sunspots of a new solar cycle, observed in 2010-2011 at the same time intervals in the optical and radio ranges. We used magnetograms from SDO/HMI with a cadence of 45 s, and radio images at a frequency of 17 GHz obtained with the Nobeyama Radioheliograph (NoRH). Radio images in intensity (Stokes parameter I ) and circular polarization (Stokes parameter V ) were synthesized with a cadence of ten seconds and ten-second averaging. Time profiles obtained with NoRH and SDO/HMI show a correlation between the radio emission of sunspots and a magnetic field. Wavelet spectra and cross-wavelet transforms give similar oscillation periods: 30-40 min, 60-70 min, 100-110 min, and 150-200 min. The same periods found by fundamentally different methods from ground-based and space observations confirm the solar nature of these oscillations. One of the possible interpretations of our results is that detected oscillations reflect eigen oscillations of a sunspot as a whole predicted by the shallow sunspot model.

Magnetohydrodynamic Oscillations in the Solar Corona and Earth’s Magnetosphere: Towards Consolidated Understanding

“…Indeed, large-scale variations with these periods are occasionally seen in different layers of the solar atmosphere in different observational bands (see, e.g. Abramov-Maximov et al 2013;Yuan et al 2011). But, association of these oscillations with flares has not been established.…”

Eigenspectra of solar active region long-period oscillations

“…The various oscillatory phenomena can be classified in different types like umbral chromospheric oscillations with a typical period of 3 minutes (Chorley et al, 2010;Centeno et al, 2006;Fleck & Schmitz, 1991;Kuridze et al, 2009), umbral photospheric oscillations with a typical period of 5 minutes (Thomas et al, 1984;, long-period oscillations with typical periods of several hours (Dumbadze et al, 2017;Efremov et al, 2007;Goldvarg et al, 2005), and ultra-long-period oscillations with typical periods of several days (Khutsishvili et al, 1998;Gopasyuk, 2004). The long-period oscillations in sunspots were discovered both in radio emission measurements and in magnetic field data (Gelfreikh et al, 2006;Efremov et al, 2007;Solov'ev & Kirichek, 2008;Smirnova et al, 2013;Abramov-Maximov et al, 2013). The ground-based and space-based observations yielded very similar long-period oscillations of sunspots that confirm the solar nature of these oscillations (Abramov-Maximov et al, 2013;Nagovitsyn & Nagovitsyna, 2011).…”

“…The long-period oscillations in sunspots were discovered both in radio emission measurements and in magnetic field data (Gelfreikh et al, 2006;Efremov et al, 2007;Solov'ev & Kirichek, 2008;Smirnova et al, 2013;Abramov-Maximov et al, 2013). The ground-based and space-based observations yielded very similar long-period oscillations of sunspots that confirm the solar nature of these oscillations (Abramov-Maximov et al, 2013;Nagovitsyn & Nagovitsyna, 2011). State-of-the-art space-based observational facilities provide data with unprecedented accuracy, which encourages both observational and theoretical studies of the physics behind the AR dynamics (Moradi, 2012).…”

Eigenspectra of solar active region long-period oscillations

“…The various oscillatory phenomena can be classified in different types such as umbral chromospheric oscillations with a typical period of three minutes , umbral photospheric oscillations with a typical period of five minutes , long-period oscillations with typical periods of several hours , and ultra-long-period oscillations with typical periods of several days ). The long-period oscillations in sunspots were discovered both in radio emission measurements and in magnetic field data Abramov-Maximov et al 2013). The ground-based and space-based observations yielded very similar long-period oscillations of sunspots that confirm the solar nature of these oscillations (Abramov-Maximov et al 2013;.…”