Amplitude variation of Pc 5 pulsations at high latitudes

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Abstract
Normal‐run magnetograms for the year 1967 from seven Canadian observatories were scaled to study the amplitude characteristics of Pc 5 pulsations. The results of the statistical analysis are: (1) Large amplitude Pc 5's occur in a limited region located on the poleward side of the auroral zone. (2) The diurnal variation of Pc 5 amplitude maximizes in the postnoon period at Resolute Bay and this peak tends to appear earlier and earlier in the day at the lower latitude stations, e.g., it appears in the morning at Great Whale River. An additional midnight peak in the diurnal variation of amplitude is noted at auroral zone stations. (3) The amplitude attains a maximum value at Great Whale River near the central line of the auroral zone. It decreases at a faster rate toward the lower latitudes than toward the higher latitudes. In quiet intervals an additional peak in the amplitude‐latitude profile is noted near the cusp region at Baker Lake. (4) The diurnal variation pattern of amplitude shows no clear relationship with the seasons or with magnetic activity. (5) Under disturbed magnetic conditions a much larger amplification of the amplitude of Pc 5's has been at Great Whale River than at high or low latitude stations. Pc 5 amplitudes correlate very well with Kp up to a level of 6−. (6) With increasing solar elevation angle the region of maximum amplitude of Pc 5 is found to move toward the northern border of the auroral zone. (7) From the data analyzed, amplitudes of Pc 5 do not show a 27‐day recurrence tendency.

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