Abstract
Comparison of the daily values of indices and parameters of solar–terrestrial physics in 2001 is made in order to allocate the most important values for future forecasts of geomagnetic activity. Changes in the indices and parameters describing all sequences of active processes from the surface of the Sun to the magnetosphere of the Earth were considered. The validity of application of the Wolf numbers as characteristics of solar activity due to sunspots is confirmed. The most geoeffective parameters depend on the arrival of the interplanetary shock from coronal mass ejection to the Earth’s orbit and the presence of the southern component of the interplanetary magnetic field with intensity values less than−20 nT. If these parameters are known in real time, about 90% of magnetic storms with sudden commencement can be forecast within 8–10 h before the start of their negative influence on the Earth.