The Magnetic Storm of May 13–17

Abstract

A TIME of unusually severe and protracted magnetic disturbance began on May 13, at about 13h. Iom. G.M.T., with an S.C. (“sudden commencement”). This was clearly oscillatory in D (declination), movements to west, east, and again west following in rapid succession, their extreme range being about 15prime;. Within about a minute of the S.C., H (horizontal force) was enhanced about 120y. The appearance of the trace suggests a very rapid preliminary fall, but this is not clear. Immediately after the large rise a fall began in H, but the element remained above its normal value for about five hours. The disturbance following the S.C. was only moderate until nearly 20h. on May 13, when considerably larger movements appeared in H. Disturbance continued throughout May 14, but there was a comparative lull between 8h. and 16h. Subsequent, however, to 16h. disturbance became very active, and the night of May 14–15 was much more disturbed than the previous night.