1. Akasofu, S.-I.: 1969, Nature
221, 1020.
2. Akasofu. S.-I. and Meng, C.-I.: 1969, J. Geophys. Res.
74, 293.
3. Alfvén, H. and Carlqvist, P.: 1967, Solar Phys. 1, 221.
4. Armstrong, J. C. and Zmuda, A. J.: 1970, J. Geophys. Res.
75, 7122.
5. Birkeland, K.: 1908, 1913, The Norwegian Aurora Polaris Expedition 1962–1963, Vol. I, First Section (1908) and Second Section (1913) Christiania.