On the geomagnetic storm effect

In a recent paper,1 an objection was raised against the “ring-current” hypothesis of geomagnetic storm effects, and an alternative hypothesis based on atmosphere displacements was advanced. The objection arose from the unacceptable delay, estimated at 87 days, required for the passage of the storm through the outer reaches of the earth's atmosphere. This delay was taken to be the diffusion time appropriate to a medium having permeability μ(= μ0 = 4π × 10−7 henry/m) and conductivity σ(∼ 1 mho/m), for penetration to a depth L(∼ 5×106 m). This relation fails to take into account the possible existence of a dominating magnetic field, such as the geomagnetic field in the present case. It fails, for example, to distinguish between the longitudinal and transverse components of the conductivity matrix (relative to the direction of the field), although the transverse components often determine the penetration properties of an electromagnetic disturbance. These components are almost certainly much less than 1 mho/m in the regions concerned, and, if inserted directly in (1), they lead to much more acceptable time delays. A criticism of a similar nature can be brought against the development of the proposed hypothesis of atmospheric displacements, though not against the hypothesis itself.