Dynamic spectra processed from data recorded on magnetic tape at the mid-latitude Ralston station (Alberta) in 1967 have been studied in detail. The Pc3,4 pulsations appear to behave in a much more complicated manner than reported by other observers at low-latitude stations. The variation of the Pc3,4 frequency at Ralston assumes different forms from one day to another, the pattern depending largely upon the general level of magnetic disturbance represented by the K(p)-index. It appears, however, that most of the Pc3,4 spectra analysed may be classified into one of, or a combination of, four well-defined diurnal patterns under steady magnetospheric conditions. An interpretation is offered to explain the existence as well as the fine structure of these four diurnal patterns. The crux of the present interpretation is that Ralston, under moderate magnetospheric agitation, may pick up micropulsation activities originating from the plasmasphere and/or the plasmatrough depending upon its position relative to the plasmapause. Eigen oscillations of modified Alfven mode (poloidal oscillation) in these two magnetospheric regions are considered to be the prime sources of the ground observed Pc3,4 magnetic pulsations. Such suggestion is reinforced by observations made simultaneously at other mid- and high-latitude stations. Other morphological properties of Pc3 and Pc4 are discussed in the light of the new interpretation. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Four portable magnetometer stations were set up at intervals of 80 - 100 kilometers along an east-west profile running from Tofino on the west coast of Vancouver Island to Abbotsford on the mainland in order to study the spatial dependence of the coastal anomaly. These were supplemented by records from the permanent Victoria Magnetic Observatory. The Tofino-Abbotsford chain extends and partly overlaps an earlier chain of stations set up to search for geomagnetic anomalies, along an east-west profile from Lethbridge, Alberta to Vancouver, British Columbia, The coastal anomaly recorded at Tofino is observed exclusively in the vertical component, diminishing rapidly inland and reaching its maximum value when the inducing field changes in approximately an east-west direction with a frequency between one and two cycles per hour. The horizontal and vertical variations are in a ratio of two to one at the coast which is in agreement with induction ratios calculated at coastlines in Australia and California. The directional dependence and limited spatial extent of the anomaly indicate a rather shallow conductivity discontinuity, at most 100 kilometers deep, running approximately parallel to the continental shelfline. Since at the maximum response frequency the upper mantle beneath the ocean is largely shielded by the overlying wedge of sea water, the anomaly is thought to be mostly due to the conductivity contrast between the deep ocean and the continent. The diurnal geomagnetic variations which pass through the surface layers virtually unattenuated show at least a twenty five percent enhancement in the vertical component from Abbotsford to Tofino. This anomaly perhaps reflects a change in upper mantle conductivity more accurately than does the higher frequency Tofino anomaly. At a still higher frequency of three cycles per hour where the Tofino anomaly is already reduced, there is a small anomaly in the vertical component at Westham Island on the east side of Georgia Strait which is completely absent at lower frequencies. The influence of a shallow body of sea water such as Georgia Strait is expected to be small. Hence this anomaly is probably due to a conductivity structure beneath the Strait in the crust or upper mantle. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate