On the theory of the first phase of a geomagnetic storm: A new illustrative calculation based on an idealised (plane not cylindrical) model field distribution

The motion of a semi-infinite neutral ionized stream in a unidirectional magnetic field of increasing intensity parallel to the stream surface is considered. The ions and electrons in the stream are assumed to be devoid of random motion so that the stream surface remains plane throughout the motion. It is shown that the particles in the stream overtake those immediately in front so that the stream surface is constantly reformed by new particles arriving from the main body of the stream. The stream is thus able to penetrate further into the field than would be the case if they were alone in the field. The retardation of the stream surface is calculated and it is shown that the rate at which the velocity of this surface decreases compares well with the calculations made by S. Chapman and the writer in 1931. It is shown that the front surface of the stream is eventually brought to rest. The difficulties envisaged by S. Chapman and the writer see 2 of “References” at end of paper regarding the electrical conductivity of the stream are shown to be illusory, as had already been concluded by the authors in 1. The sudden increase in the horizontal force, H, above the mean over a period of about two minutes is here identified with a sudden commencement (SC) of a geomagnetic storm. The curve illustrating the rise in H shows considerable similarity to the curves of SCs derived on “quick-run” magnetic records.