Oblique h.f. radiowave propagation in the main trough region of the ionosphere

Abstract

The propagation of 7-335 MHz, c.w. signals over a 5212 km sub-auroral, west-east path is studied. Measurements and semi-empirical predictions are made of the amplitude distributions and Doppler shifts of the received signals. The observed amplitude distribution is fitted with one produced by a numerical fading model, yielding the power losses suffered by the signals during propagation via the predominating modes. The signals are found to suffer exceptionally low losses at certain local times under geomagnetically quiet conditions. The mid-latitude trough in the F2 peak ionization density is predicted by a statistical model to be at the latitudes of this path at these times and at low K p values. A sharp cutoff in low-power losses at a mean K p of 2 75 strongly implicates the trough in the propagation of these signals. The Doppler shifts observed at these times cannot be explained by a simple ray-tracing model. It is shown however, that a simple extension of this model to allow for the trough can reproduce the form of the observed diurnal variation.

Seasons of MISTs and mellow fruitfulness

“…This is a highly undesirable phenomenon for all concerned and one that the older scientist can help prevent. Incidentally, that first talk of mine was eventually published (Lockwood & Mitchell 1980) and has been cited just the once in 38 years. This overview gives me an opportunity to double that total at a stroke, and one that I am shameless in taking.…”