A test of two theories for the low-frequency cutoffs of nonthermal continuum radiation

A discussion and analysis of two theories that differently identify the low-frequency cutoffs of nonthermal continuum radiation are presented. The cold plasma theory and an alternate one proposed by Jones (1976) are compared experimentally with the use of continuum radiation data obtained in the outer magnetosphere by the Imp 6 and ISEE 1 spacecraft. It is found that the characteristics of this specific radiation are consistent with those expected of ordinary and extraordinary mode waves described by the cold plasma theory and it is shown that the cutoff frequencies occur at the local plasma frequency and R = 0 cutoff frequency as proposed by the same theory. The inconsistencies which were found between the Jones theory (1976) and observation are presented, and in addition no evidence is found for a component of continuum radiation propagating in the Z mode in the outer magnetosphere.