Divergence of Radio Rays in the Ionosphere

Abstract

Travelling disturbance manifestations on ionosonde records usually occur at different times on the "o" and "x" traces. It is shown that this is due to the divergence of the ordinary and the extraordinary rays in the Earth's magnetic meridian plane and that the sense of this time difference, therefore, gives a direct indication of the sense of the north-south component of movement of the disturbance. Furthermore, where the direction and speed of travel of a disturbance can also be determined from spaced station observations, the actual separation of reflection points of the o- and the x-rays can be deduced. At Sydney, N.S.W. (33° 52' S., 151° 11' E.) this is of the order of 30 km at the height of maximum ionization of the F2 region. On h't records the corresponding time difference observed includes a component due to the vertical separation of reflection points if the front of the disturbance is not vertical. From records of this type taken at three spaced stations the horizontal component may be determined directly. Examination of some 430 such observations taken over a period of 4 years confirms the variation of the time difference with direction of travel predicted by theory, and also indicates the consistent presence of a forward tilt in the front of disturbances.