The characteristics of solar flare type (s.f.) variations of the geomagnetic field at Huancayo, Kakioka, and Watheroo are statistically examined. The main indicators of these characteristics are the time from beginning of a s.f. variation to its maximum deviation (T1), and the ratio of its maximum deviation to the range of daily variation at the corresponding time (ΔH/RH). With respect to both quantities, the data of the three stations show nearly the same values. The magnitude of the s.f. variations at Huancayo is abnormally large, butT1and ΔH/RHshow normal values.Assuming that the s.f. variation has an abrupt increase, the integrated electrical conductivity of the ionosphere is estimated with the aid of a theoretical calculation of transient dynamo‐action. The result shows that the integrated conductivity of the ionosphere amounts to 6×10−8∼7×10−8emu. over those t