Features of Excitation of Stimulated Electromagnetic Emission of the Ionosphere Modified by an Oblique High-Power Radio Wave

We present the results of measuring the characteristics of the stimulated electromagnetic emission (SEE) of the ionosphere with variation in the zenith angle of a pump beam of high-power O-mode radio waves in the geomagnetic-meridian plane. The experiments were performed at the midlatitude heating facility “Sura.” It is established that the maximum intensity of the DM and BC components of SEE is observed for southward inclination angles θ ≈ 8°--12° of the antenna beam, for which the most intense generation of artificial small-scale ionospheric irregularities also takes place. Based on the results of measurements near the fourth and fifth harmonics of the electron gyrofrequency, it is found that the first component of the BUM (BUM-1) is generated only when the pump wave reaches the plasma-resonance region. This allows one to assume that, unlike the second component of the BUM (BUM-2), whose generation is determined by development of instability in the upper-hybrid resonance region, the BUM-1 generation mechanism should be related to processes of interaction between a high-power radio wave and the plasma in the plasma-resonance region. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 743–756, September 2005.