Abstract
ONE of the very great magnetic storms, the most violent recorded at this observatory since that of September 25, 1909, commenced quite suddenly at 6.50 G.M.T. on August 11 from a very slightly agitated normal curve, in both the elements of declination and horizontal force. The H magnet increased sharply by 84γ (1γ≡10-5 C.G.S. unit), and the D magnet swung 10′ to the west. The direction of motion in each element was immediately reversed, with a very rapid decrease of 113γ in H, and a swing in D, equally rapid, to the east of 16′. After a few very rapid swings the spot of light due to H decreasing went off the recording drum at 7 a.m., and remained off until it returned at 7.24 G.M.T. At 8.12 G.M.T. H increased rapidly, the range of the swing exceeding 446γ. At 8.50 G.M.T. it again decreased rapidly, the spot of light remaining off the recording drum until 9.43 G.M.T. These oscillations in H were accompanied by rapid swings in D. After its sudden increase and decrease at the beginning of the storm it swung 60′ to the west. At 8.52 G.M.T. it was 50′ in the opposite direction. The extreme range in D during the storm was 110′, and of H, since the spot of light travelled off the drum on either side, greater than 780γ.
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CORTIE, A. The Magnetic Storm of August 11–12, 1919. Nature 103, 483 (1919). https://doi.org/10.1038/103483a0
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DOI: https://doi.org/10.1038/103483a0
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