HF ray propagation in the presence of resonance heated ionospheric plasmas

Abstract

The process of formation and further evolution of strong electron concentration inhomogeneities in the F-layer of the ionosphere created by the field of a powerful radio wave is investigated. Numerical simulations are employed to obtain the associated ray propagation trajectories which determine communication properties under such circumstances. The simulations involve the formulas obtained for the problem of one-dimensional non-stationary thermo-diffusion and diffusion spreading of the electron component for ionospheric plasmas. The numerical model takes into account the real boundary conditions in the E- and F-layers of the middle-latitude ionosphere and the altitudinal distribution of electron transport coefficients, as well as the ionization-recombination balance in the ionosphere. The ray tracing model is introduced to examine changes of the probing waves trajectories due to reflections from heating induced ionospheric plasma inhomogeneities at various ranges. Using the extended Hamiltonian formulation for the ray equations, the changes of ray trajectories passing through the heating area in the upper ionosphere are examined for different regimes of ionospheric plasma heating. The results show that local resonance heating is conducive to broader bandwidth and that, in the presence of sharp gradients, reflection takes place at higher frequencies than in the quiescent ambient ionospheric plasma. It has been found that in certain cases reflection occurs well into the 1 GHz band. This result is important for both communications between ground based stations and for wave propagation involving low altitude missiles and satellites or re-entering space vehicles. It was found that, for adaptive heating which is closely related to natural phenomena in the high latitude ionosphere, the effect of bandwidth broadening is less meaningful. The ray propagation algorithm used takes into account the loss properties of the plasma medium, although it has been found that for the presently simulated parameters these effects are marginal.