Abstract:
It is well known that the daily international magnetic character figure Ci constitutes a valuable index for classifying days according to their magnetic activity averaged over a large part of the earth. As a measure of the intensity of geomagnetic disturbance, Ci is in fact comparable to the Zurich relative sunspot number S, which is a recognized measure of solar activity. Daily Ci values are available in an unbroken sequence from 1884 onwards.