1. Balasubrahmanyan, V. K., et al, 9th Intl. Cosmic Ray Conf. (London), 1, 427, 1965.
2. Burger, J. J., and Swanenburg, B. N., Geophys. Res.(Space), 78, 292, 1973.
3. Burlaga, L., et al., Geophys. Res.(Space), 90, 12027, 1985.
4. Chih, P.-P., and Lee, M. A., J. Geophys. Res.(Space), 91, 2903, 1986.
5. Cummings, A. C., et al., 13th Intl. Cosmic Ray Conf. (Denver), 1, 335, 1973.