MULTISITE OBSERVATIONS OF VLF TRANSEQUATORIAL PROPAGATION ANOMALY

Phase and amplitude records of 18.6‐kHz transmissions from NPG/NLK received at eight sites varying in distance from 4,360 to 13,420 km southwest of the transmitter, confirm the existence of a region within ±20° of the magnetic equator, in which VLF propagation parameters vary significantly from their midlatitude values. At all seven sites that involved transequatorial propagation paths, anomalies (including cycle slipping) were observed during the sunrise transition. The nature and temporal occurrence of these anomalies depended on the distance of the receiver from the magnetic equator. The experimentally derived dependence on magnetic latitude of the mode conversion ratio of the two least attenuated propagating modes and their apparent interference spacing are presented. Copyright 1969 by the American Geophysical Union.