Solar and geomagnetic activity on a long time scale: Reconstructions and possibilities for predictions

Using two mathematical methods based on the wavelet transform and nonlinear dynamics, we reconstructed the behavior of the aa-index of geomagnetic activity in the past. Two versions of the series are provided: for the last 400 years and on an almost 1000-year time scale. We consider typical values of the aa-index at grandiose extrema of solar activity. The same high level of geomagnetic activity as that observed in the last 50 years is shown to have also taken place in the early 12th and late 14th centuries. We suggest an extended time series of A-indices of the large-scale solar magnetic field. On the 400-year time scale, we confirmed that the large-scale magnetic field develops earlier than the magnetic fields of active regions. Ohl’s prediction method was verified on the same time scale.