Search

The spatial dynamics of microwave emission (data from the Nobeyama Radioheliograph) of active regions with a complex magnetic field configuration before powerful flares, as well as the fine structure of active sources of ultraviolet (UV) emission based on AIA/SDO data, are studied. It is shown that there is unsteady behavior of microwave sources, along with the ignition of a system of crossed UV loops (X-structures). A class-M X-ray flare occurs after several hours at the site of ignition of the intersecting UV loops. The similar behavior observed in microwave and ultraviolet emission in the five active regions studied by us likely serves as a sign of a preflare situation in the active region on the Sun. [ABSTRACT FROM AUTHOR]

This paper is a study of the spatial dynamics of microwave emission (data from the Nobeyama Radioheliograph) from two active regions NOAA 12673 and NOAA 11261 for several hours prior to powerful class M x-ray flares. The spatial distribution of the radio brightness and emission intensity in certain parts of the active region is found to be highly nonstationary. Data in the ultraviolet (AIA/SDO) are also used for studying the fine structure of the active emission sources. It is shown that the spatial dynamics of the microwave sources correlates well with the position and appearance of bright ultraviolet (UV) loops in the 94 Å line, i.e., with magnetic loops where the plasma is heated to high temperatures ~107 K. A combined analysis of the UV and radio emission charts with magnetic field charts (HMI/SDO) for NOAA 12673 shows that the highly nonstationary behavior of the microwave sources develops simultaneously with the ignition of a system of intersecting UV loops (X-structures). It is also shown that the bright UV loops and microwave sources arise in the area where new magnetic fluxes emerge. [ABSTRACT FROM AUTHOR]

A three-dimensional simulation of the microwave emission of nonthermal electrons within a flare magnetic loop that takes into account the influence of the chromosphere has been carried out. The paper investigates the possibility of the generation of a microwave spectrum (observed for some solar flares) with a maximum in the centimeter wavelength range and a positive slope in the millimeter one under the some distribution of the magnetic field strength and the parameters of the anisotropic nonthermal electrons along the loop. By the example of the event on July 5, 2012, it is shown that nonthermal electrons can be responsible not only for the centimeter bell-shaped emission spectrum generated in the coronal part of the loop but also for the increasing millimeter spectrum generated in the chromosphere. [ABSTRACT FROM AUTHOR]

The ordinary mode of gyrosynchrotron radiation was identified to be predominant in some segments of flare loops in solar flares of July 19, 2012, and October 22, 2014. These events were studied by investigation of the quasi-transverse propagation effect on the observed polarization. The analysis involved reconstruction of the magnetic field topology at the linear force-free approximation based on the data of the SDO HMI space telescope and the subsequent simulation of radio emission of flare loops with the GX Simulator software package. The quasi-transverse propagation effect was established to be characteristic for both events, but its influence on the radio emission polarization at a frequency of 17 GHz was observed only in the October 22, 2014 flare. [ABSTRACT FROM AUTHOR]