Memoirs of the Kakioka Magnetic Observatory Vol.06 No.01， p.67, April, 1951
External Field of Geomagnetism
In order to investigate the external field of earth magnetism, the magnetic potentials uniformly magnetized are expanded using the annual values (1922-36) at the magnetic observatories in the world. The coefficients of potential show note worthy correspondence with the relative numbers of sunspots, but the amplitudes in a solar cycle are only 10 gamma or more. On the other hand, the electron densities are reported to change by amount of about 50% in F2 layer in which the external field may be probably produced on account of low collisional frequency.
From these results, the external field cannot be produced at least in F2 layer or below in the ionosphere.