Extremely Low Frequency (ELF) field strength measurements made in Connecticut during 1976

Horizontal magnetic field strength measurements (both amplitude and relative phase) at 76 - or- 4 Hz were made in Connecticut from August to December 1976 to further investigate sunrise, daytime, sunset, nighttime, and seasonal extremely low frequency (ELF) propagation variations. The transmission source for these 1.6 Mm range measurements was the U.S. Navy ELF Wisconsin Test Facility (WTF). The principal observations obtained from these measurements were (1) that ELF nighttime propagation is much more variable than daytime propagation, (2) that the nighttime field strength amplitude usually minimized around 0600 to 0800 GMT, whereas the nighttime relative phase maximized about an hour earlier, (3) that increases in geomagnetic activity were usually accompanied by decreases in the minimum nighttime field strength, (4) that the repetition rate between the lowest measured minimum nighttime field strengths was nearly equal to the solar rotation period, (5) that the 'Halloween effect' was observed for the seventh year in a row, (6) that the average relative phase difference between daytime and nighttime propagation conditions was 22 degrees, which corresponds to a relative phase velocity difference delta (c/v) of 0.15, (7) that phase velocity changes occurring during nighttime propagation conditions occasionally are greater than changes associated with the sunrise-sunset terminators crossing the transmitter or receiver locations, and (8) that large decreases in field strength amplitude were not accompanied by large decreases in effective atmospheric noise levels.