Giant micropulsations at Abisko

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Abstract
At the Geophysical Observatory of Abisko, Swedish Lapland, a set of Toepfer variometers has been in operation since midsummer 1921, with a break of one month only in October to November 1927, when more rigid mountings were made. The time‐scale has been 20 mm per hour and sensitivities of 5γ in eastward, 10γ in northward, and 8γ in vertical component per mm most of the timeThe portions of records reproduced in Figure 1 were obtained on September 10 and 12, 1930, and illustrate a special kind of rare perturbation, which occurs distinctly only three or four times a year at Abisko. Its characteristic feature is a regularly emerging and vanishing sinusoid with period of order of one minute. With more sensitive instruments, somewhat regular pulsations are not uncommon, and their existence is well known to scientists even at lower latitudes. My first acquaintance with similar phenomena dates back to August 1914, when in charge of the temporary magnetic station erected in connection with the solar eclipse at Strömsund, Central Sweden. Professor V. Carlheim‐Gyllensköld at once directed my attention to the explanation of Eschenhagen's “Elementarwellen” given by Professor C. Störmer2 in 1906. The sensitivity in the Strömsund records for all elements was about 1.67 per mm, and in a fortnight similar micropulsations were conspicuous several times with a range of about 1γ. The pulsations of September 12, 1930, at Abisko, however, had ranges of 14γ in the northward component, 34γ in the eastward, and 23γ in the vertical component. True giant amongst dwarfs! There were about 50 full swings with a mean period of 111 seconds, and the phenomenon lasted for 1 hour and 27 minutes.

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