1. Backus, G., R. Parker, and C. Constable, Foundations of Geomagnetism, Cambridge University Press, 1996.
2. Chapman, S. and J. Bartels, Geomagnetism, Oxford University Press, 1940.
3. Engels, U. and N. Olsen, Computation of magnetic fields within source regions of ionospheric and magnetospheric currents, J. Atmos. Sol.-Terr. Phys., 60, 1585–1592, 1998.
4. Gray, C. G., Multipole expansion of electromagnetic fields using Debye potentials, Am. J. Phys., 46 (2), 169–179, 1978.
5. Jackson, J. D., Classical Electrodynamics, 2nd Ed., Wiley, New York, 1975.