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 a symptotic formulas and numerical simulations, allowing for a wide variety o f 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 propa gating high-frequency radio waves. By means of a numerical simulation it is shown that, for typical fine structure parameters, the upper boundary of t he operating frequency range can be increased by 1.5-2 MHz through the scat tering by irregularities. The study revealed previously unknown regions whe re the influence of random irregularities upon the radio wave propagation i s enhanced dramatically in consequence of the ray field defocusing in a reg ular 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 bei ng extended through the scattering of upper rays. (C) 1999 Elsevier Science Ltd. All rights reserved.