1. Akioka, M., Kubota, J., Suzuki, M., Ichimoto, K., and Tohmura, I.: 1987,Solar Phys. 112, 313.
2. Bai, I.: 1987,Astrophys. J. 314, 795.
3. Belmont, A. D., Dartt, D. G., and Ulstad, M. S.: 1966,J. Atmospheric Sci. 23, 314.
4. Bogard, R. S., Bai, T., Cliver, E. W., and Kile, J.: 1989,Bull. Am. Soc. 21, No. 2.
5. Cartes Synoptiques de la Chromosphère Solaires: 1931?1964, published by Observatoire de Paris, Section d'Astrophysique at Meudon.