Time series of the annual and monthly average Wolf numbers and aa geomagnetic-activity indices for 1868-1990 are studied using the method of sliding cross-correlation analysis. In addition to the analysis of aa indices, we also study the annual numbers of 3-h intervals with different activity levels - those of a quiet state (the aa index does not exceed 4) and of a disturbed state (the aa index is no less than 30). Variations in the coefficient of the linear 23-year sliding correlation between the Wolf numbers and the parameters of geomagnetic activity, with a period of -40-50 years, are distinguished. The analysis of sliding cross-correlation functions shows that the distinguished decadal variations of the correlation are due to variations in the time delay between the indices of solar and geomagnetic activity, from 0 to ∼3 years. The mean time delay of geomagnetic activity with respect to solar activity for the entire interval considered is ∼1 year. A possible explanation for the results obtained is the alternation of periods during which the ratio of contributions of the two main components of geomagnetic activity varies with time; these two components are associated the solar-flare streams and the generation of high-sped solar-wind streams in the coronal holes.
|Number of pages||5|
|Journal||Geomagnetism and Aeronomy|
|State||Published - 1999|