An investigation of magnetic pulsations at Canadian magnetic observatories

More than 1,000 pulsations, with approximately constant periods and ranges exceeding 3 gammas, have been studied using Meanook and Agincourt standard run magnetograms for the years 1951 to 1954. This investigation confirms the existence of two separate classes of pulsations, differing in form, time of diurnal occurrence, and mean period. Some additional characteristics reported earlier from Scandinavia are confirmed, but it is now thought that the narrow band Rolf micropulsations are not infrequent ~ 1200 kms. south of the auroral zone in Canada. Very few regular pulsations \1·ere observed on magnetograms from stations north of the auroral zone. Although magnetohydrodynamic waves in the upper parts of the ionosphere provide a possible periodic explanation, the different times of occurrence of the classes in Scandinavia and Canada, and even across Canada, the relationship of the primary sources of pulsations to magnetic disturbance measured by K-indices, and the southern geomagnetic extension in Canada of observable pulsations remain unexplained. Screening effects in the lower ionosphere are considered and provide one explanation of the observed amplitude-period trend.