1. Polar-cap absorption;Bailey;Planet. Space Sci.,1964
2. Midday recoveries of polar cap absorption;Leinbach;J. Geophys. Res.,1967
3. Tables and maps of geomagnetic coordinates corrected by the higher order spherical harmonic terms;Hakura;Rep. Ionos. Space Res. Japan,1965
4. Polar blackouts associated with severe geomagnetic storms on Sept. 13, 1957and Feb. 11, 1958;Hakura;Rep. Ionos. Res. Japan,1958
5. Enhanced ionization in the polar ionosphere caused by solar corpuscular emissions;Obayashi;Rep. Ionos. Space Res. Japan,1960