Evening?Type Transequatorial Propagation on Japan?Australia Circuits

Abstract

The correlation between the reception in the evening of v.h.f. signals on Japan Australia circuits and the presence of spread F along the circuits is examined. The correlation is found to be highly significant and leads to the conclusion that spread F is a necessary but not sufficient condition for such reception. The fact that the presence of spread F is not a sufficient condition is explained in terms of either breaks in its distribution along the circuits or of plasma frequencies which are too low to support the proposed propagation mode.