Ionospheric heating by powerful radio waves

In addition to the communication applications that stem from the generation of field‐aligned irregularities, ionospheric heating by powerful HF waves also holds promise for establishing new techniques in D ‐, E ‐, and F ‐region aeronomy. This paper concentrates on the application of the theory of plasma heating by ohmic and nonlinear dissipation to the special conditions of the lower ionosphere where the electron collision and disturbing wave frequencies are comparable and the upper ionosphere where electron thermal transport is large and restricted by the earth's magnetic field. We predict the magnitude and distribution of large‐scale changes in the electron temperature and density in both the D and F layers under a variety of conditions. These results are compared with direct measurements or inferred changes whenever possible. We also examine the effects of specular‐height mismatch, multiple frequency operation involving heater‐power sharing, and antenna beam tilt on the total cross section for field‐aligned scattering. The analysis is based on the concept that the energy‐density distribution on the heater reflectrix computed by means of a ray‐tracing technique can be related directly to the density‐fluctuation intensity through an appropriate scattering model. Lastly, potential applications to aeronomy are discussed, particularly in regard to D ‐region measurements of the effective recombination coefficient magnitude and temperature dependence and the relative water cluster ion concentration.