The Quiet Sun at cm- and mm-Wavelengths

Soon after the first detection of radio emission from the sun two components of the solar radio radiation were identified: The emission related to active centres on the disk and the radiation of the undisturbed, static solar atmosphere, in which the active regions are embedded. The undisturbed component is observed to vary only slightly during the solar sunspot cycle, it is called the emission of the quiet sun. A theoretical estimate of this component was first given by Martyn (1946) and subsequently developed in more detail by many other authors. The basic observations were performed with poor angular resolution. Still at present most experimental data are taken with angular resolutions of about 1 to 4 arc min, too low to discriminate between the different solar atmospheric fine structures, clearly seen in various spectral lines. The quiet component of the solar radio radiation therefore represents the average emission of an inhomogenous solar atmosphere.

Mode Coupling in the Solar Corona. I. Coupling Near the Plasma Level

The theory of mode coupling in the radiation from solar type I storms is extended to treat coupling when the frequency! is near the plasma frequency!p. It is found that Cohen's coupling ratio Q = U/It)4, where It is the transition frequency (f'P It for strong coupling), is to be multiplied by a factor (1-!~/ J2)5/2 for QT regions, i.e. coupling is relatively suppressed close to the plasma level. The implications on the handedness of solar radio radiation are discussed. The possibility of depolarization due to mode coupling is considered briefly.