Spectral studies of the time-series of the geomagnetic activities

The geomagnetic effect of active centers of the Sun has been investigated statistically dividing into three groups according to the values of — Bo of the active centers and using the method of superposed epochs. Some interesting results between active centers and recurrent and sporadic storm days have been found; that is, recurrent storm days do not increase significantly while the frequency of sporadic storm days increases when the active centers approach to the Sun-Earth line. We have also investigated new periodicities of aa, Ap and Ci indices using Discrete Fourier Transforms, and have found some new periodicities and confirmed the known ones.