1. Etude expérimentale de l'anomalie ionosphérique équatoriale en Afrique en période de minmum solaire;Vila;Ann. Géophys.,1966
2. private communication at a meeting of URSI's “World Wide Soundings Committee” held at Leningrad;Besprozvannaya,1970
3. Electron density models of the ionosphere;Köhnlein;Rev. Geophys. Space Phys.,1978
4. World-wide dayly variations in the height of the maximum electron density of the ionospheric F2 layer;Shimazaki;J. Radio Res. Labs.,1955