Occurrences of rapid micropulsations at Sodankylä during 1932 to 1935

The rapid micropulsations, which are discussed herein, are shown in quick‐run records of terrestrial magnetism and earth‐currents as characteristic and easily distinguishable widenings of the curves, the shape of which is often reminiscent of that of a short shuttle. Single oscillations cannot be determined by the records, since the maximum period of an oscillation is less than 2 or 3 seconds—an interval not shown on the timescale of 180 mm per hour. Figure 1 gives reproductions of records, obtained February 6, 1935, of oscillations of this kind in magnetic declination and in both components of earth‐currents. Even a casual glance at the records reveals that rapid micropulsations occur in groups, and only from time to time. Usually they take place in the course of a few consecutive days, after which sometimes a week, or even a month, may pass before new oscillations occur. It is seldom that such an oscillation occurs singly; usually there is a number of oscillations, interrupted by short intervals, for one hour, for several hours, sometimes even for more than 24 hours continuously, when the curve often resembles a pearl necklace consisting of oval pearls of different sizes.