Anomalous Sunrise Effects Observed on a Long Transequatorial VLF Propagation Path

One year's observations of VLF transmissions from NLK received over a long transequatorial path at Smithfield, South Australia, are described. Phase cycle slipping on this path is common and is shown to be an integral part of the direct path modal interference pattern during the sunrise transition. The seasonal variation of cycle slipping and the sunrise fading is shown to be a function of the angle made by the propagation path with the sunrise line. The occurrence of phase cycle slipping and the associated fade spacing anomalies are interpreted as arising from anomalously high mode conversion when the sunrise line is in the vicinity of the geomagnetic equator.