Extreme values in ionospheric radio propagation

Proposals are made for Earth-space and space-space paths to apply the term ‘propagation degradation probability’, analogous to ‘basic circuit reliability’ adopted within the Radiocommunication Sector of the International Telecommunication Union (ITU-R) to quantify the performance of HF terrestrial ionospheric radio circuits. The principal elements characterising propagation impairments are described and formulae and a table given by the ITU-R are reproduced relating many of these effects to the path total electron content. Expressions are provided enabling estimates of the probabilities of occurrence of user-specified extreme values to be estimated in terms of their median quantities and day-to-day variabilities. The need is stressed for additional data collection and analyses both to refine the median values and to derive the required reference variability factors.