| The interaction of high power, high frequency radio waves with the lower ionosphere is becoming an area of considerable theoretical and experimental interest. In particular, significant ohmic heating of the collisional, weakly ionized ionospheric plasma is possible, which can change the absorptive and conductive properties of the plasma in a non-linear fashion. Precisely controlled heating may have applications to the production of ELF/VLF waves in the ionosphere by the stimulation of natural current systems, which may find uses in remote sensing, scientific, military, and communications fields. However, due to the lack of a valid kinetic model and experimental data on the temperature effects of heating, the efficiency of the potential ionospheric radiator remains largely undetermined.; This dissertation presents a theoretical study of the heating process based on a fluid (equilibrium) formulation, and an experimental study designed to test the model. Incoherent scatter radar experiments were conducted at the Arecibo Observatory to measure altitude profiles of electron temperature changes due to heating. Experimental evidence shows for the first time that the electron distribution may become non-Maxwellian under the influence of high frequency radio waves, even at relatively modest power levels. The skewed distribution is thought to affect the rate of heat input into the plasma, and ultimately the steady-state electron temperatures in the case of sustained heating. |
