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The study involves the obtainment of regular tracers of the solar cycle in the radio range by activity manifestations in the chromosphere and corona. Our research method consists of the systematic processing of the RATAN-600 radio data at frequencies 3–18 GHz obtained during more than one cycle of solar activity and their comparison with other databases of time series characterizing the magnetic activity of the Sun at the photospheric level. In the first phase of this work, we identified an array of approximately 600 active regions that evenly covers all phases of solar cycle 24 in approximately 9 years, for which we reliably identified the local radio sources based on RATAN-600 data, as well as data from other databases, such as spacecraft of the Space Weather Prediction Center of the National Oceanic and Atmospheric Administration and the Solar Dynamics Observatory. The sample is statistically homogeneous and evenly distributed over solar latitudes in both hemispheres. The statistical relationships between the sunspot areas and the parameters of intensity and polarization of local radio sources are obtained. It is shown how the spectral flux density of local radio sources in the chromosphere and corona at different frequencies increases with the increase in the sunspot area (and, consequently, the magnetic flux). The estimates of exponents of this dependence are obtained. [ABSTRACT FROM AUTHOR]

The distributions of temperature and density in the sunspot atmosphere are crucial for an understanding of the process of energy transfer from the photosphere upward to the corona in strong magnetic fields. The joint analysis of millimeter observations at ALMA (Atacama Large Millimeter/Submillimeter Array) and observations performed in the microwave range (centimeter wavelengths) with the RATAN-600 radio telescope of the Russian Academy of Sciences provides new data on the temperature distribution and physical processes at different altitudes above a spot. The NOAA 12470 active region was observed and mapped at 1.3 and 3 mm (ALMA) and 2–10 cm (RATAN-600) in December 2015. These observations are analyzed, and the results are compared to models of sunspot atmospheres. The fundamental problems arising in the study of atmospheres of active regions in the millimeter and centimeter ranges are determined, and the importance of the 3–18 mm range in the physics of the generation and transfer of energy for corona heating is demonstrated. [ABSTRACT FROM AUTHOR]

Spectral polarization observations of radio sources above sunspots are regularly carried out with the RATAN-600 radio telescope (RATAN is a Russian acronym for the Radio Astronomical Telescope of the Academy of Sciences). The in-depth studies of the spectra reveal new effects. In this paper, we analyze the manifestation of radio emission of the fourth gyrofrequency harmonic in microwave spectra obtained with 1-percent frequency resolution in a range of 3–18 GHz. Registration of the extraordinary mode in the short-wavelength range of the spectrum is compared to the model calculations of the second-to-fifth gyrofrequency harmonics against a background of the thermal bremsstrahlung emission of flocculi, surrounding the spot structure of an active region. The brightening of the extraordinary mode in the short-wavelength spectral range and the kinks in the intensity spectra of emission are analyzed. The interpretation of the RATAN-600 observational data with probable diagnostics of the emission of the fourth gyrofrequency harmonic is considered as examples. [ABSTRACT FROM AUTHOR]

A CME/flare event occurred at the eastern limb on 25 January, 2007. Seven successive multi-wavelength scans in the range 1.8 cm – 5.0 cm were obtained with the RATAN-600 radio telescope starting just at the beginning of the post-eruptive arcade formation (30 min after a C6.3 flare peak) and lasting for 3.5 hours. The conditions were favorable to study the off-limb microwave radio source associated with the post-eruptive arcade in different phases of its formation. Microwave radio emission of the arcade was rather intense initially and then considerably decreased; its maximum was co-spatial with the 195 Å Fe xii loop tops. The RATAN-600 total flux spectra of the off-limb radio source were practically flat during the first two hours indicating a predominant contribution of thermal emission. The X-ray spectrum was thermal (according to RHESSI data) at that time. Data available in the meter wavelength range during this phase were indicative of weak non-thermal processes likely due to accelerated particles. However, free – free emission of an isothermal source dominated in microwaves. This is indicative of the presence of a large amount of plasma in the region of arcade formation at the initial stage of the event. The weak microwave emission during the decay phase might be interpreted as the thermal cyclotron emission of the loops in the arcade. [ABSTRACT FROM AUTHOR]

We develope a method to compute the temperature and density structure along the line of sight by inversion of the differential emission measure (DEM), under the assumptions of stratification and hydrostatic equilibrium. We apply this method to the DEM obtained from the Atmospheric Imaging Assembly (AIA) observations and use the results, together with potential extrapolations of the photospheric magnetic field, to compute the microwave emission of three sunspots, which we compare with observations from the Academy of Sciences Radio Telescope - 600 (RATAN-600) radio telescope and the Nobeyama Radioheliograph (NoRH). Our DEM-based models reproduce very well the observations of the moderate-size spot on October 2011 and within 25% the data of a similar sized spot on March 2016, but predict too low values for the big spot of 14 April 2016. The latter is better fitted by a constant conductive flux atmospheric model which, however, cannot reproduce the peak brightness temperature of 4.7×106K and the shape of the source at the NoRH frequency. We propose that these deviations are due to the low intensity non-thermal emission associated to a moving pore and to an opposite polarity light bridge. We also find that the double structure of the big spot at high RATAN-600 frequencies can be interpreted in terms of the variation of the angle between the magnetic field and the line of sight along the sunspot. [ABSTRACT FROM AUTHOR]