An apparatus for recording the dynamic spectrum of high-intensity solar radiation (in particular the sudden bursts) in the frequency range 70-130 Mc/s. is described. The spectra are displayed on a cathode-ray tube at intervals of about one-third of a second. Solar bursts observed with the apparatus were found to have widely different spectra. However, analysis of a number of bursts indicated the common occurrence of three distinct spectral types. These types are described and illustrated by samples. One type, of narrow bandwidth, was exhibited by short-lived bursts that occur in large numbers during periods of high intensity ( ?noise storms?) ; these bursts are presumed to be circularly polarized and associated with sunspots. A second type, characterized by a slow drift of spectral features towards the lower frequencies, was exhibited by sporadic " outbursts " associated with solar flares. Other sporadic bursts had diverse spectra, but some of them conformed to a third spectral type in which the frequency of maximum intensity drifts rapidly towards the lower frequencies. The result that outbursts seem to exhibit a distinct type of spectrum is considered to provide a possible means of recognizing these phenomena with certainty.
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Wild et al. (1950) studied this question.