1. Howard, R. and Koomen, M.: 1973, EOS Trans. AGU 54, 1192.
2. Howard, R. and Koomen, M.: 1974, Solar Phys. 37, 469.
3. Rosenberg, R. L. and Coleman, P. I.: 1969, J. Geophys. Res. 74, 5611.
4. Sawyer, C.: 1974, Geophys. Res. Letters 1, 295.
5. Svalgaard, L.: 1974, ?Solar-Terrestrial Physics and Meteorology?, A working document (ed. by SCOSTEP secretariat), pp. 72?84.