The interannual modulation of the solar and geomagnetic activity relationships

Abstract

The interannual modulation of the geomagnetic activity caused by solar activity is investigated by means of the mutual spectral analysis. The frequency characteristics of connection between the Wolf numbers W 0 and the aa index of geomagnetic activity for the time interval 1890-1990 are analysed. Interannual and seasonal variations in the corresponding coherence spectra CH(T ) for the quasi-decennial, quasi-pentennial, quasi-triennial and quasi-biennial cycles are revealed. The particular properties of the mean parameters for individual months are outlined.