Ionospheric Modelling and HF radio systems at high latitudes

Successful planning of HF radio systems to operate at high latitudes requires some means of predicting ionospheric morphology, both as regards ambient electron density and ionospheric irregularities causing backscatter. Because of the presence of several physical processes, and the sparsity of data, reliable statistical models are not easily constructed. However, increasing knowledge of the processes operating, and the availability of powerful computers, makes the construction of physically-based numerical models of ionospheric structure a viable proposition. Such a model at a fairly advanced stage of development is described. Examples of calculated electron densities are given. The ingredients and shortcomings of the model are be described, together with the steps to be taken to account for ionospheric irregularities, and to allow us to predict HF system performance using ray-tracing.