On the Diurnal Variation of the Periods of Pc3, 4 Micropulsations

The period has been measured of each cycle of all Pc3, 4 micropulsation occurring on 10 days selected from a month's rapid run records collected during July-August, 1968 at four Canadian observatories. The periods are averaged over each hour and then the hourly values are averaged in two groups of five days according to the Cp value for the days. For Pc3 on the quieter days the diurnal variation of the periods shows a maximum peak near local noon while on disturbed days the variation changes to ‘U-type’ with the minimum period near noon. The Pc4 period is found to be lowest in the morning and highest in the evening at Ottawa and Meanook. But at higher latitudes (Baker Lake and Resolute Bay) the Pc4 period variation is simply ‘U-type’. Analysis also shows the presence of a diurnal variation of the correlation between Pc periods and Kp. The position of the plasmapause seems to determine Pc4 periods except at the higher latitudes while effects closer to the ionosphere may have a greater influence on the periods of Pc3 pulsations.