Effects of large-scale clouds of ionospheric irregularities on the propagation of high-frequency radio waves

We have devised a technique for computing the radio wave scattering using asymptotic formulas and numerical simulations, allowing for a wide variety of electron density profiles of a regular ionosphere. For a model ionosphere containing, against a background of regular layers, large-scale clouds of ionization with small-scale fine structure, a study is made of the effects due to the signal scattering into the skip zone produced by obliquely propagating high-frequency radio waves. By means of a numerical simulation it is shown that, for typical fine structure parameters, the upper boundary of the operating frequency range can be increased by 1.5-2 MHz through the scattering by irregularities. The study revealed previously unknown regions where the influence of random irregularities upon the radio wave propagation is enhanced dramatically in consequence of the ray field defocusing in a regular ionosphere. For paths with the hop range close to a limiting range, it is shown that there is a fundamental possibility of the reception zone being extended through the scattering of upper rays. (C) 1999 Elsevier Science Ltd. All rights reserved.