RATAN-600 measurements of the 2-4 CM radio brightness distribution over the disk of the quiet sun

Observations of the sun with the RATAN-600 radio telescope at five wavelengths (2.0-4.0 cm) and with resolution ranging from 17 arcsec x 13 arcmin to 33 arcsec x 25 arcmin indicate that the brightness temperature Tb is distributed uniformly over the disk out to 0.95 solar mass. At 4.0 cm there is a limb brightening effect of equal to or less than 10%, weakening toward shorter wavelengths. The value of Tb drops to one-half at a radius ranging from 1.024 solar mass (wavelength 2.0 cm) to 1.052 solar mass (wavelength 4.0 cm); Tb = 400 K, 1500 K, respectively, at 1.1 solar mass. This behavior indicates that the structure of the chromosphere-corona transition zone and the inner corona is decidedly inhomogeneous.