The Physical Image of Various Solar Radio Emissions

Solar radio emissions (SREs) originate primarily from electrons—both thermal and non-thermal—in the solar atmospheric plasma. Owing to the diverse physical conditions (e.g., temperature, density, and magnetic field) across different source regions, as well as variations in electron acceleration processes, number densities, energies, and propagation directions, SREs can be broadly categorized into three main types: quiet radio emission (QRE), slowly varying component (SVC), and solar radio bursts (SRBs). SRBs are further subdivided into type I, II, III, IV, and V bursts. Moreover, each SRE type is frequently superimposed with various spectral fine structures, which encode signatures of chromospheric and coronal heating, non-thermal electron acceleration, and plasma instabilities associated with solar activity (flares, coronal mass ejections, filament eruptions, and various jets). Based on a brief review of SREs, this work presents a unified physical image to illustrate the formation of all SRE types and their interrelationships. This image aims to clarify the physical processes revealed by these emissions, elucidate the origin and evolutionary patterns of solar activity, and provide critical clues for forecasting catastrophic space weather events.