A SCENARIO for the FINE STRUCTURES of SOLAR TYPE IIIb RADIO BURSTS BASED on ELECTRON CYCLOTRON MASER EMISSION

Abstract

A scenario based on electron cyclotron maser (ECM) emission is proposed for the fine structures of solar radio emission. It is suggested that under certain conditions modulation of the ratio between the plasma frequency and electron gyro frequency by ultra-low-frequency waves, which is a key parameter for excitation of ECM instability, may lead to the intermittent emission of radio waves. As an example, the explanation for the observed fine-structure components in the solar Type IIIb bursts is discussed in detail. Three primary issues of Type IIIb bursts are addressed: (1) the physical mechanism that results in intermittent emission elements that form a chain in the dynamic spectrum of Type IIIb bursts, (2) the cause of split pairs (or double stria) and triple stria, and (3) why only IIIb-III bursts are observed in the events of fundamental harmonic pair emission whereas IIIb-IIIb or III-IIIb bursts are very rarely observed.