Long Time Oscillations of Wolf Number Series Autocorrelation Function   and Possibility of Solar Activity Prediction
  Results of analysis of long time variations of solar activities based on monthly Wolf number series (1749-2011 years) are represented. Shown the presence of stable oscillations in autocorrelation function for the Wolf numbers series with a period near 42.5 years. The statistical model of variations of autocorrelation function based on assumption of nonstationarity process are constructed. The question of using the model to predict the solar activity is discussed. 
V. M. Zhuravlev and S. V. Letunovskiy
astro-ph.SR physics.data-an