Radio propagation systems have to cope with plasma properties encountered along ray-paths within the ionosphere

Radio propagation systems have to cope with plasma properties encountered along ray-paths within the ionosphere. Both large-scale spatial gradients and small-scale irregularities affect reliable use of radio systems for communications and navigation. Some of the most severe horizontal gradients within the ionosphere are caused by magnetospheric processes. One example is the inner magnetosphere´s plasmapause. This feature has as its ionospheric signature the equatorward wall and minimum of the F-layer´s main (sub-auroral) trough in electron densities and total electron content (TEC). Satellite-based radio diagnostics revealed that the gradients associated with the trough´s equatorward and poleward boundaries are strongly altitude dependent. Such “topside sounder” observations can be made only along a satellite´s orbital track, and thus longitudinal consistency of trough signatures must come from other means. Maps of TEC from ground-based networks monitoring GNSS signals extend trough coverage in longitude (local time). Yet, depending on the spacing of the terrestrial receivers, accurate specification of trough gradients and locations can be under-estimates of the actual gradients.