Friday, May 13 1921: At peak of the 15th solar cycle, Solar activity increases.

1921 (Taisho 10) May 13 (Friday) – 15th (Sunday) The 15 th solar cycle peak. Solar activity increases and anomalies are observed all over the world. Aurora was observed in the zenith in addition to the communication failure in California by the large-scale magnetic storm. The signal and switching system of the New York Railroad completely stopped, and the switchboard of the control tower was destroyed and a fire occurred. Telephone and telegraph connections were also disrupted in Europe.

In Japan, too, the horizontal gauge needle of Kakioka Magnetic Observatory swung downward and became unobservable, which was published in English by Shinichi Kunitomi (28), an engineer at Kakioka Magnetic Observatory who just obtained a doctorate of science in Tokyo Imperial University in the previous year, and attracted attention in the world. Shinichi Kunitomi “The Magnetic Storm of May 13 -17, 1921 as observed at the Kahioha Magnetic Observatory.” Journal of the Meteorological Society of Japan. Ser.I, vol. 40, issue 7, pp. en3-en 6