Thermal Bremsstrahlung of Local Sources Over Solar Spots Based on Microwave Observations

Abstract

The paper presents the results of a study of microwave thermal bremsstrahlung of local sources above sunspots. Special attention is paid to the transition from thermal bremsstrahlung to the dominant gyroresonance radiation in the high-frequency part of the spectrum of 12–20 GHz (1.5–2.5 cm). At high frequencies, for which the magnitude of the magnetic field is not enough to generate gyroresonance radiation, thermal bremsstrahlung is the main factor. The presented calculations demonstrate an increase in brightness in an extraordinary mode and a decrease in its intensity in an ordinary mode, as well as corresponding examples of observations. The possibilities and advantages of determination of the field with one polarization corresponding to ordinary radiation are revealed. The studied spectral-polarization features of the radiation, estimates of the effective radiation height, and the characteristic features of the change in the sizes of sources with the wave frequency will make it possible to correctly interpret the observations and to improve the accuracy of magnetic field measurement and the diagnostics of the transition region temperature.