1. 1. Akasofu, S.-I., Space Sci. Rev., 19, 169, 1970
2. 2. Alcaydé, D., Technical Rpt. 97/53, EISCAT Scienific Assoc., Kiruna, Sweden, 1997
3. 3. Basu, S. and K.M. Groves, in: Space Weather, P. Song, H.J. Singer and G.L. Siscoe (Eds), American Geophys. Union, Washington, D.C. 2001.
4. 4. Chapman, S. and J. Bartels Geomagnetism, Vol. 1 and 2, Oxford, Clarendon Press, 1962
5. 5. Collis, P.N. and M.T. Rietveld, Ann. Geophysicae, 8, 809-824, 1990.