1. Bendat, J. S. and Piersol, A. G.: 1971, Random Data: Analysis and Measurement Procedures, Wiley-Interscience, New York.
2. Cini Castagnoli, G. and Bonino, G.: 1985, Nuclear Tracks 10, 759.
3. Cini Castagnoli, G. and Bonino, G.: 1988, in G. Cini Castagnoli (ed.), Solar-Terrestrial Relationships and the Earth Environment in the Last Millennia, Proc. of the Int. School of Physios ?E. Fermi?, Course XCV (1985), Elsevier, Amsterdam, p. 317.
4. Cini Castagnoli, G., Bonino, G., and Provenzale, A.: 1988a, Nuovo Cimento 11C, 1.
5. Cini Castagnoli, G., Bonino, G., and Provenzale, A.: 1988b, Solar Phys. 117, 187.