Relations between electron contentand peak density: regular and extreme behaviour

Electron content statistics offers important information for planning and operation of various application
systems that make use of the transionospheric propagation of radio signals. Electron content statistics
meet with an important difficulty: the majority of data stem from observations on the radio signals of orbiting satellites. The database for vertical electron content derived from observations of radio signals
emitted from geostationary satellites is only very small. Therefore it is important to make use of statistics for peak density from ionosonde measurements. Quantile statistics do not contain information about ionization extremes. Therefore it is necessary to complement the statistics with case studies which reveal unusual and extreme electron content structures in space and in time.