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In this study, a comparative analysis was carried out on the preflare and flare conditions for six flares accompanied by coronal mass ejections (CMEs) and five events not accompanied by CMEs. All of the events occurred in the period 2011–2014. The features of the spatial dynamics of microwave emission of active regions (data from the Nobeyama Radioheliograph) prior to the selected events and during flares were studied. For the same 11 events, the fine structure of active ultraviolet (UV) sources was examined based on SDO/AIA data. Certain differences were found in the behavior of microwave emission for events with CMEs. The features of the frequency radio spectra from the RATAN-600 data were found for some active regions. [ABSTRACT FROM AUTHOR]

The time delays between sub-terahertz (sub-THz) and soft X-ray (SXR) emission from solar flares with a positive spectrum slope at frequencies of >100 GHz are considered. Based on a cross-correlation analysis of the time profiles of sub-THz and SXR emission from 11 flare events obtained from the KOSMA (230 GHz), SST (212 GHz), and RT-7.5 (93 GHz) telescopes, as well as the GOES satellite in channel 1–8 Å, we identified two main types of sub-THz events. Type I includes four X-class events with a well-defined Neupert effect, i.e., the sub-THz flux outpaces the SXR flux by 2–9 min. Type II includes seven M-class flares, in which the time profiles behave similarly and the delays do not exceed 30 s. The different mechanisms of radio emission in different layers of the solar atmosphere may be responsible for the positive slope of the sub-THz spectrum of flares. [ABSTRACT FROM AUTHOR]

The temporal evolution of thermal bremsstrahlung in the sub-terahertz range is calculated for F-CHROMA models of the flare chromosphere and transition region (https://www.fchroma.org). These models are calculated based on the numerical solution of the system of equations of radiation hydrodynamics with the RADYN code, which describes the response of chromospheric plasma to the flux of accelerated electrons in the form of a triangular pulse. It is found that the positive slope of the spectrum in the frequency range of 93–400 GHz is formed during the entire burst. The sub-THz radiation peak can be both ahead and behind the maximum of the function of the injection of energetic electrons depending on the number and index of the spectrum of precipitating particles. In some cases, the time profile of the sub-THz radiation is quite complex and pulsating due to gas-dynamic phenomena in the chromosphere and transition region. [ABSTRACT FROM AUTHOR]