| Summary: | Airlines use the polar routes because for some flights the shortest route (the great circle) takes them over the polar regions. However, a lack of VHF ground stations over the oceans and within polar regions means that aircraft have to rely on long-range HF communications via the ionosphere. The ionosphere is affected by space weather more intensively in the high latitude regions. In severe space weather conditions, ionospheric HF communications become impossible, and aircraft have to be re-routed to lower latitudes. This increases the flight time, cost, passenger and flight loadings and impact on the environment. The research reported in this thesis designs a model of HF propagation that can provide nowcasting (and forecasting) to advice airlines of the likely quality of HF communications. The model consists of electron density profile, ray-tracing, and signal loss and antenna gain considerations. An electron density model partially comprises a background ionosphere, and the work presented in this thesis contributes by proposing an assimilative model based on the International Reference Ionosphere (IRI). This is then perturbed by ionospheric structures that occur within the high latitudes regions. Ionospheric absorption is then applied, and the gain at both antennas (transmitter and receiver) included. Finally, maps of signal coverage are generated for a specific date, time and frequency. Assessment of IRI model was discussed through comparisons of the prediction with the standard IRI model. Comparisons revealed improvements in foF2 using IRI. The predicted HF signal characteristics have been compared with the observations. The model shows an ability to yield results with good agreement with the observations. Features were reproduced through the model for two periods: one showing the influence of an absorption event, and the other experienced much off great circle propagation. A method of using the output of the nowcast model has been introduced with examples.
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