ELF Propagation Irregularities on Northern and Mid-Latitude Paths

Summary of extremely low frequency (ELF) field strength measurements made in Connecticut during 1975

“…It has been postulated [Davis, 1974[Davis, , 1976; Spjeld-vik and Thorne, 1975a, b] that levels of the D region controll•g ELF propagation in the earth-ionosphere waveguide are strongly influenced by energetic electron precipitation. Recently reported measurements [Wratt, 1977;Dickinson and Bennett, 1978] are consistent with the theoretical results of Soejeldvik and Thorne [1975a, b] regarding ionization caused by precipitation of energetic electrons during the recovery phase of magnetic storms.…”

ELF Field Strength Measurements Made in Connecticut During 1974

“…In many cases, there is a definite correlation between ionospheric irregularities and the lower-than-normal measured nighttime field strengths. [19][20][21][22] During the last few years , we have made a considerable number of horizontal magnetic field strength measurements in Connecticut . One fact that we have definitely noticed is that ELF nighttime propagation is much more variable than ELF daytime propagation -both in variations from night to night and throughout each nighttime measurement period .…”

Localized ELF nocturnal propagation anomalies

“…On several occasions during the past decade, the 40-80 Hz ELF nighttime field strength measured at sites in the northeastern United States (i.e., Connecticut and Maryland) has displayed rapid decreases of from 4 to 8 dB in several hours [Bannister, 1974[Bannister, , 1975[Bannister, , 1979bBannister et al, 1974Bannister et al, , 1980Bannister and Williams, 1976;Davis, 1974Davis, , 1976. These severe nighttime disturbances sometimes occur during the several days following magnetic storms when similar but less pronounced behavior is found to coincide a Now occupying Applied Physics Chair, Naval Postgraduate School, Monterey, California 93940.…”

“…It has been postulated [Sechrist, 1972;Davis, 1974Davis, , 1976Spjeldvik and Thorne, 1975a, b] that levels of the D region controlling ELF propagation in the earth-ionosphere waveguide are strongly influenced by energetic electron precipitation. Recently reported measurements [Wratt, 1977;Dickinson and Bennett, 1978] are consistent with the theoretical results of Spjeldvik and Thorne [1975a, b] regarding ionization caused by precipitation of energetic electrons during the recovery phase of magnetic storms.…”