Observations of coronal holes with the Siberian Radioheliograph

Abstract

Multi-wavelength observations of a coronal hole (CH) with two-dimensional spatial resolution have been made for the first time in the frequency range from 2.8 to 12 GHz. At frequencies below 6 GHz, the average brightness of the hole is 1.5 times lower than the brightness level of the quiet Sun. The distribution of radio brightness over the hole is inhomogeneous: the ratio of maximum to minimum brightness temperatures falls from several times at low frequencies to tenths of fractions at the upper received frequencies. At frequencies above 6 GHz, the temperature contrast between the CH and regions of the quiet Sun is small. Within the CH, there are compact sources that are bright relative to the quiet Sun. In general, observations of CHs with SRH are promising both for the research into the nature of CHs and for the applied problems of forecasting solar wind characteristics.