Excitation of short-wave oscillations in the ionospheric plasma by the field of a high-power radio wave with extraordinary polarization due to induced scattering by ions

Abstract

We analyze excitation of electron-cyclotron or upper hybrid oscillations of the ionospheric plasma at a frequency that is close to the pump frequency as a result of induced scattering of a high-power radio wave with extraordinary polarization by ions. The excited oscillations have a small wavelength of the order of the Larmor electron radius, which allows them to propagate near and below the reflection level of an extraordinary radio wave. We found the instability increment and threshold field, which results from collisional absorption of plasma waves. It is shown that the threshold field is minimal near the reflection level of an extraordinary radio wave when the radio wave frequency f0 is between electron harmonics nfBe with n≥2. In an ionospheric F layer it is of the order of 1 W/m. Such fields are easily obtained in ionospheric heating experiments allowing for radio-wave field swelling in the reflection region. In the vicinity of electron harmonics fo≅nfBe, the threshold field is increasing. For fo<nfBe with fo≅nfBe the instability does not develop because of the absence of plasma oscillations with a frequency that is close to the pump frequency (the latter also refers to the case fo<2fBe). The expressions obtained are generalized to the case in which the instability under consideration is excited by the field of an ordinary radio wave in the region of its quasilongitudinal propagation. We discuss the possibility of using the emergence of very short-wave plasma oscillations for explaining the experimentally observed phenomena.