Ad-753 162 Radiation Induced F-region Plasma Phenomena

Collective plasma phenomena induced in the ionospheric F-region by intense high-frequency radiation are examined on several time and length scales. The short wavelengh, high-frequency turbulence associated with the observed high-frequency enhanced electron density fluctuations at the electron plasma frequency is shown to result from parametric excitation of plasma and acoustic waves by the highfrequency radiation. The wave kinetic equation describing the nonlinear evolution or the turbulence is presented. The time asymptotic spectral intensity ii» calculated and a formula for the total energy absorption from the incident radiation via nonlinear collective effects is obtained. A radiation induced self-focussing instability is found on a length scale somewhat larger than an ion Larmor radius, and is offered as a possible explanation for the occurrence of magnetic field aligned density filaments, which are associated with the phenomenon of "artificial Spread-F." The calculated growth rates are in agreement with the time delay for appearance of spread-F after modifier turn on.