1. Indices of geomagnetic variations and the ionospheric disturbances;Gulyaeva;Adv. Space Res.,1992
2. Criteria for ionospheric storminess,1944
3. A Review of Daily Ionospheric Indices: Current Status and Recent Innovations;Wilkinson;IPS Technical Report IPS-TR-86-02,1986
4. Voting procedure for distinction of geomagnetic quiet and disturbed conditions at the ionospheric data analysis and modelling;Gulyaeva;Publicaciones del Observatorio del Ebro, Memoria # 16,1992