Abstract
Solar activity is studied using a cluster analysis of the time-fluctuations of sunspot number. In the historic period (1850–1932) the cluster exponent α≃0.37 (strong clustering) for the high-activity components of the solar cycles. In the modern period (last seven solar cycles: 1933–2007) the cluster exponent was α≃0.50 (random, white-noise–like). Comparing these results with the corresponding data from laboratory experiments on convection it is shown that in the historic period the emergence of sunspots in the solar photosphere was dominated by turbulent photospheric convection. In the modern period, this domination was broken by a new more active dynamics of the inner layers of the convection zone. Cluster properties of the solar-wind magnetic field and the aa-geomagnetic-index also support this result. Long-range chaotic dynamics in the solar activity is briefly discussed.