Solar radio burst spectral observations, particle acceleration, and wave-particle interactions

We consider solar radio bursts throughout the radio spectrum from 30 kHz to 30 GHz. While the range of phenomena over this spectral range is large, the subject can be conceptualized by considering three characteristic frequencies of the plasma: the plasma frequency fp, the gyrofrequency fB, and the frequency f(tff = 1) at which the plasma becomes optically thick due to bremsstrahlung. We present an overview in terms of these characteristic frequencies to show why each dominates under various physical conditions in the Sun and solar wind. In the broad regime where plasma emission dominates, we discuss the progress that has been made in explaining the observed burst characteristics theoretically, concentrating on bursts of type II (shock wave related) and type III (excited by electron beams). Moving then to microwaves, we show that the microwave spectrum contains considerable diagnostic information, but that present observations cannot access it except in rare cases when the burst is spatially simple. We conclude with a discussion of future prospects for making further progress in the study of solar radio bursts.