1. Bell, M. B. and Kennedy, W. A. G.: 1974, Publ. Astrophysics Branch, National Research Council Canada, 1, No. 4.
2. Chapman, R. D. and Neupert, W. M.: 1974, J. Geophys. Res. 79, 4138.
3. Chiuderi-Drago, F., Furst, E., Hirth, W., and Lantos, P.: 1975, Astron. Astrophys. 39, 429.
4. Covington, A. E.: 1974, J. RASC 68, 31.
5. Covington, A. E. and Bell, M. B.: 1973, World Data Center A, Report UAG 28, Editor, E. G. Coffey, Part 1, 168, NOAA, Boulder, Colo.