Memoirs of the Kakioka Magnetic Observatory Vol.06 No.01， p.42, April, 1951
On the Storms of Earth-Current Potentials observed at Kakioka
In the period of 1934 to 1942, 266 sudden commencement storms of earth-current potentials were recorded at Kakioka. Their mean storm-time variation is similar in its general feature as that in geomagnetism. The amplitudes of sudden commencement and maximum ranges of storms are obtained, and the frequency curves of direction and duration of sudden change at the time of occurrence are also obtained; their values are E10°N and 3.5 minutes, respectively. Mean duration of storms are 30 hours.