Sudden transitions and grand variations in the solar dynamo, past and future^☆

¹ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, The Netherlands
² Departamento de Física, Facultad de Ingenieria, Universidad de Buenos Aires, 1428 Buenos Aires, Argentina

^* corresponding author: e-mail: info@cdejager.com

Received: 21 February 2012
Accepted: 11 June 2012

Abstract

The solar dynamo is the exotic dance of the sun’s two major magnetic field components, the poloidal and the toroidal, interacting in anti-phase. On the basis of new data on the geomagnetic aa index, we improve our previous forecast of the properties of the current Schwabe cycle #24. Its maximum will occur in 2013.5 and the maximum sunspot number R_max will then be 62 ± 12, which is within the bounds of our earlier forecasts. The subsequent analysis, based on a phase diagram, which is a diagram showing the relation between maximum sunspot numbers and minimum geomagnetic aa index values leads to the conclusion that a new Grand Episode in solar activity has started in 2008. From the study of the natural oscillations in the sunspot number time series, as found by an analysis based on suitable wavelet base functions, we predict that this Grand Episode will be of the Regular Oscillations type, which is the kind of oscillations that also occurred between 1724 and 1924. Previous expectations of a Grand (Maunder-type) Minimum of solar activity cannot be supported. We stress the significance of the Hallstatt periodicity for determining the character of the forthcoming Grand Episodes. No Grand Minimum is expected to occur during the millennium that has just started.