Title: Self-focusing of intense radio waves in the ionosphere
Abstract: Nonstationary self-focusing of electromagnetic waves under the action of Ohmic heating is investigated for anisotropic inhomogeneous plasmas. This mechanism may be responsible for field-aligned structure generation by intense radio waves in the ionosphere, which, in turn, gives rise to observed artificial spread-F ionospheric striations and high-frequency scattering. For a vertical geometry, a linearized analysis is given providing a field-aligned filamentation rate as a function of perturbation transverse wavelength, incident power, and plasma parameters. For typical ionospheric parameters and incident flux of 50 μW/m2, exponentiation times of the order of 5 sec are obtained for transverse wavelengths of the order of a kilometer.