Theory of the modulation imposed on an obliquely incident radio wave reflected in a disturbed region of the lower ionosphere

Abstract

A powerful disturbing wave enters the lower ionosphere and causes a periodic modulation of the electron collision frequency. A simple model is adopted for this disturbed region. The modulation transferred to an obliquely incident wanted wave that is reflected in or near it is investigated. The reflexion coefficient of the wanted wave is found by applying the phase integral method. The complex reflexion height of the wanted wave is a function of time in the modulation cycle. Results are discussed first for an isotropic ionosphere and are then extended to include the effect of the Earth’s magnetic field, and the calculation uses the Booker quartic equation. It is shown that the phase integral method is admirably suited to solve this kind of problem. Some examples are given to illustrate that the greatest amount of modulation is transferred when the wanted wave is reflected near the most disturbed part of the ionosphere. The relation of this to some observed effects near sunrise is discussed.