A Model for the Sources of the Slowly Varying Component of Microwave Solar Radiation.

Abstract

view Abstract Citations (164) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Model for the Sources of the Slowly Varying Component of Microwave Solar Radiation. Kakinuma, T. ; Swarup, G. Abstract A comparison of the observations of the slowly varying component of the solar radio emission made with high-resolution interferometers operating at wavelengths of 3 2, 7.5, 9.1, and 10.7 cm shows that the flux densities of many strong sources are higher at the longer wavelengths than at 3 cm. The same conclusion is derived from eclipse and statistical investigations, which indicate further that the spectrum of the flux density has a peak around 6 cm. The decrease in flux density with frequency cannot be explained simply by assuming a greater optical thickness for the extraordinary wave near 10 cm in the million-degree corona, as given by the magneto-ionic theory, since the observed degree of polarization at 7 5 or 9 1 cm is much lower than that at 3.2 cm. It is suggested that radiation at the gyro-frequency and its harmonics emitted by the thermal electrons in the dense region over a sunspot group should be taken into account to explain the spectrum of the slowly varying component. This mechanism of resonance absorption requires the average strength of the magnetic field over the sunspot group to be about 600 gauss at a height of 2 x 10 km above the photosphere and 250 gauss at a height of 4 x 10 km In order to explain the observed values of brightness temperature of 1 x t K near 10 cm by the magneto-ionic theory, it is necessary to assume values of electron density of up to 20 or 40 times the normal However, these high values of densities are not required by the gyro-theory, and values of five to ten times the normal are sufficient for explaining simultaneously the observations of brightness temperature, flux density, and polarization. This theory also explains the small size of the source in the range 3-10 cm The radio emission is considered to originate thermally, which requires that the value of the electron temperature in the region of the inner solar corona above a large sunspot group is about 2 x . Publication: The Astrophysical Journal Pub Date: November 1962 DOI: 10.1086/147450 Bibcode: 1962ApJ...136..975K full text sources ADS |