Memoirs of the Kakioka Magnetic Observatory Vol.01 No.01， p.1, March, 1938
Atm.Elec.Potential-Gradient at Kakioka
Annual and diurnal variation of calm days at the surface during five years，1931-1935, are studied. The morning maximum occurs about two hours after sunrise, and the beginning of the peak is about one and half hour earlier than its apex. The effects of wind and cloud upon the potential gradient are considerable. On the days of continuous wind the potential gradient generally shows low value; morning maximum is greatly decreased except summer months, and the time of its occurrence is retarded about one hour, while the evening maximum scarcely appears.