New evidence of anomalous transequatorial ionospheric propagation

Echoes of exceptionally long delay detected by a H. F. radar located in the West Indies are interpreted as ground backscatter propagated by two successive reflections from the F-region of the ionosphere, without intermediate ground reflection. Propagation of this sort between two points on the earth requires an initial ionospheric tilt followed by one of opposite sign. Tilts of the required sort take place regularly in equatorial regions as a consequence of two daily bulges in the ionosphere, one occurring at approximately 1900 local time over the geomagnetic equator, and the other occurring around noon in the vicinity of the sub-solar point. It is shown that tilt-supported propagation can take place at frequencies considerably in excess of the MUF predicted in the usual way. It is believed that these results may explain the reports by radio amateurs of anomalous propagation between North and South America.