Long-Term Changes in Sunspot Activity, Occurrence of Grand Minima, and Their Future Tendencies

摘要

Long-term changes in the magnetic activity of the Sun were studied in terms of the empirical mode decomposition that revealed their essential modes. The occurrence of grand minima was also studied in their relation to long-term changes in sunspot activity throughout the past 11 000 yr. Characteristic timescales of long-term changes in solar activity manifest themselves in the occurrence of grand minima. A quantitative criterion has been defined to identify epochs of grand minima. This criterion reveals the important role of secular and bicentennial activity variations in the occurrence of grand minima and relates their amplitudes with the current activity level, which is variable on a millennial timescale. We have revealed specific patterns in the magnetic activity between successive grand minima which tend to recur approximately every 2300 yr but occasionally alternate with irregular changes. Such intermittent activity behavior indicates low dimensional chaos in the solar dynamo due to the interplay of its dominant modes. The analysis showed that in order to forecast activity level in forthcoming cycles, one should take into account long-term changes in sunspot activity on a ≈2300-yr timescale. The regularities revealed suggest solar activity to decrease in the foreseeable future.