HF ray propagation in the presence of resonance heated ionospheric plasmas

The process of formation and further evolution of strong electron concentra tion inhomogeneities in the F-layer of the ionosphere created by the field of a powerful radio wave is investigated. Numerical simulations are employe d to obtain the associated ray propagation trajectories which determine com munication 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 ionospheri c plasmas. The numerical model takes into account the real boundary conditi ons in the E- and F-layers of the middle-latitude ionosphere and the altitu dinal distribution of electron transport coefficients, as well as the ioniz ation-recombination balance in the ionosphere. The ray tracing model is int roduced to examine changes of the probing waves trajectories due to reflect ions from heating induced ionospheric plasma inhomogeneities at various ran ges. Using the extended Hamiltonian formulation for the ray equations, the changes of ray trajectories passing through the heating area in the upper i onosphere are examined for different regimes of ionospheric plasma heating. The results show that local resonance heating is conducive to broader band width 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 sate llites or re-entering space vehicles. It was found that, for adaptive heati ng which is closely related to natural phenomena in the high latitude ionos phere, the effect of bandwidth broadening is less meaningful. The ray propa gation algorithm used takes into account the loss properties of the plasma medium, although it has been found that for the presently simulated paramet ers these effects are marginal. (C) 1998 Elsevier Science Ltd. All rights r eserved.