Sudden commencements and sudden impulses in geomagnetism: Their diurnal variation in amplitude

Summary Following on the examination of the frequencies of S. Cs. and S. Is. given in a recent paper (1), the diurnal variation of theH-amplitudes at the six stations Cheltenham, Tucson, San Juan, Honolulu, Huancayo and Watheroo during the period 1926–46 is investigated, and in this S. Cs. and S. Is. do not appear to differ greatly in their behaviour. Except in the case of Huancayo, the greatest amplitudes occur near 0h. local time, after which there is a fall to the lowest values about 7h. The S. Is. amplitudes may have a secondary minimum near 18h., but this is not certain.