Microwave Observations of Coronal Holes at the 25th Solar Cycle

Studies of the microwave emission of coronal holes and coronal hole's like areas have a significance in order to understand features of the solar activity, to analyse distributions of plasma parameters in the solar chromosphere and corona and to evaluate origins of the space weather creation. The radio telescope RT-32 of Ventspils International Radio Astronomy Centre (VIRAC) provides routine 2D cartography of the polarized microwave emission of the Sun in wavelengths of 7.5-2.3 cm (4.1-14.2 GHz) with the low noise multichannel spectral polarimeter. The paper and the conference presentation concern to the comparison of features of some characteristic coronal holes observed with the VIRAC RT-32 radio telescope in 2019-2020 and 2024-2025 (the minimum and the maximum of 25th solar cycle) in order to evaluate its visibility and a possibility of a detection of coronal holes after “single dish” microwave observations of the Sun.