Spectral distributions of microwave bursts

The lack of open literature publication of the distributional properties of the cm- lambda spectra of solar microwave bursts has led to some erroneous concepts of the typical characteristics of these spectra. To provide more accurate information, this paper sets forth various distributions of the peak flux density spectra of large numbers of bursts, based on observations of the Sagamore Hill Radio Observatory at nine discrete frequencies between 245 and 35,000 MHz over the years 1968-1971. As a foundation for the distribution studies, the basic spectral classification system is outlined. The majority of burst spectra were found to contain a cm- lambda component having a single spectral maximum in the 1400- to 35,000-MHz range; such spectra are designated C type. A study of the correlation of the spectral maximum frequency f sub(m) sub(a) sub(x) of the cm component and the photospheric magnetic field strength of the associated region shows a tendency for greater correlation at higher f sub(m) sub(a) sub(x) for stronger magnetic fields. A study of the correlation of C type spectra between f sub(m) sub(a) sub(x) and the quasi-cutoff frequency f sub(q) sub(c) on the low frequency side shows that, for bursts of moderate peak flux density (50-500 sfu), f sub(q) sub(c) is well correlated with f sub(m) sub(a) sub(x) ; a good fit to the relation f sub(m) sub(a) sub(x) = Af sub(q) sub(c) is found with A = 3.4. The possible attenuating mechanisms responsible for the spectral shaping of the cm component are discussed.