This is a report of so me particular c harac teristi cs of unique natural electromagnetic field varia tions in the frequ ency range of 3.3 cis to 0.15 cis obse rved at the earth' s surface. The signals usually exhibit a rising frequency fin e st ru cture but variat.ions are observed . The mid period and emission ele ment rec urrence period of an event are linearly related. The bursts of activity usually last about 1/2 hr, but a gross recurre nt patte rn may persist, on rare occasions, as long as 12 hr. Pulsations asso ciated with field lines reaching the greater radial di stances occur near the noo n meridian ; midfre quencies are lower at this tim e. S ignals are generally not simultaneous at most high latitude stations in the same hemispheres, but th e world level of high activit y usually persist for seve ral days. AJ though no seasonal or 27day solar controlled periodi city was observed the emissions are more likely to occur during high solar activity and in the week following large major magnetic di sturbances. No ionospheric effects associated with the fi eld variations were clearly found . Although no great differ ence in the number of events was noticed for high and middle latitudes, there was a scarcity of such signals at the equator . Conjugate point stations show uniquely similar activity. There may be an alternation of the fin e stru cture betwee n sta tions in oppos ite hemi spheres on the same earth 's mag ne tic field line. In the high latitudes, the magnetic flux de nsity vector of the e mission appears to de scribe a plane perpendicular to the earth's field li ne, polarized in a co unter clockwise se nse, and elliptically elongated in the N-S direction.
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Campbell et al. (1965) studied this question.