Magnetic Storm and Aurora on February 9–10


A MAGNETIC storm was recorded at the Kew Observatory (National Physical Laboratory) on the afternoon of February 9 and early morning of February 10 larger than any that has occurred since October 31, 1903. The curves were slightly disturbed during the whole of February 9, but the storm may be regarded as commencing with a rapid movement of a few minutes of arc in the declination needle at 2.15 p.m., with a synchronous sudden rise of 45 γ (1 γ =0.00001 C.G.S.) in the horizontal force. The storm lasted an unusually short time, being practically over by 3 a.m. on February 10, but several large rapid movements were recorded. The largest declination movement occurred between 8.19 p.m. and 8.45 p.m. on February 9. During these twenty-six minutes the needle moved 57 to the west and then 73′ to the east, the extreme westerly position being reached at 8.34 p.m. The most easterly position during the storm was reached at about 10.55 p.m., when the trace was off the sheet for a few minutes. The range during the storm actually shown on the sheet was 1° 38′. Between 1.13 am. and 1.45 am. on February 10 the needle moved steadily, without sensible oscillation, to the west, this movement reaching 1°. The rate of movement was practically uniform from 1.13 am. to 1.33 am., when it accelerated so suddenly that the curve resembles two straight lines inclined at a finite angle.

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CHREE, C. Magnetic Storm and Aurora on February 9–10. Nature 75, 367 (1907) doi:10.1038/075367a0

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