The Spatial Distribution of Rapid Geomagnetic Fluctuations: Part II

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A detailed examination has been made of some examples of rapid irregular magnetic field changes which occurred during a typical geomagnetic storm, selected from 180mm/h recordings. The following points were noted:
1. At a number of different times of day, the rapid irregular changes at a given observing station were extremely various. They varied widely in form, and loops ranged in shape from nearly linear ones to crude circles.
2. During a chosen interval, the rapid irregular changes at neighbouring stations were very similar, and between mid-latitude stations 1200 km apart there was still a strong relationship between the changes occurring during defined time intervals.
3. Phase differences between stations, during the chosen interval, were very small. The average phase gradient North to South was less than 0.5 ∼ 10–⁷ s/cm. There was a suggestion of an average phase gradient East to West of the order of 10–⁷ s/cm.
4. Vector diagrams of increments between selected times indicated large scale patterns in which the horizontal vectors tended to converge, the points of convergence being variable in position. To this extent, the changes examined cannot be distinguished either from micropulsations or from slow irregular variations.
5. Some of the evidence suggested a type of current circulation which either travelled eastwards as a whole, or spread in extent, while pulsating in amplitude.
6. The average phase gradient East to West and the suggestion of an eastward moving current circulation, both referring to daylight hemisphere changes, are reminiscent of a deduction by Dungey concerning propagation of waves on the Chapman-Ferraro surface.     

The Effect of an Ocean on Magnetic Diurnal Variations

Summary. Theoretical calculations have been made for the idealized case in which an ocean is approximated by an infinitely long rectangular conducting sheet. The results indicate that even in the case of magnetic variations with periods as long as 24 hr one should expect a significant and easily observable enhancement in the vicinity of the edge of an ocean. When the inducing field is a function of local time only, it is found that the amplification of the variations is greater at the eastern edge of the ocean than at the western edge.
Laboratory model studies have been used to investigate the effect of irregularities in the shape of a coastline. Results which have been obtained from a model of the Pacific Ocean in the neighbourhood of Japan indicate that it is reasonable to attribute at least a part of the anomalous diurnal variations observed in central Japan to electric currents induced in the ocean.