Abstract
Reviewing important classical results of studies on the geomagnetic solar flare effect (s. f. e.), it is confirmed that the geomagnetic s. f. e. is a temporary augmentation of the geomagnetic daily variation field in the sunlit hemisphere. By taking into account the electromagnetic induction within the ionosphere, it is then stressed that the geomagnetic s. f. e. be considered as a transient phenomenon in the ionosphere having about 5×10-8 emu in integrated conductivity.
Results of analyses of global distribution of 15 typical s. f. e. 's during the IGY have shown that (a) an almost perfectly simultaneous relationship holds among optical and radio solar flares, geomagnetic s. f. e. 's and sudden ionospheric disturbances; (b) a geomagnetic s. f. e. of small amplitude takes place in the dark hemisphere always simultaneously with an s. f. e. in the sunlit hemisphere; and (c) the maximum peak of s. f. e. does not always occur simultaneously at different locations but it is more retarded with increasing solar zenith distance in the sunlit hemisphere for some weak s. f. e. The two new characteristics of s. f. e., (b) and (c), are interpreted as results of transient increase in the electric conductivity of the lower ionosphere in the sunlit hemisphere caused by an X-ray solar flare.
