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Nordita Astrophysics seminars

A new simple dynamo model with cross helicity for the solar activity cycle

by Dr Nobumitsu Yokoi (Institute of Industrial Science, University of Tokyo)

122:026 ()


A new simple model for the solar activity cycle is proposed. The present model differs from the previous ones mainly in two points. First, in addition to the helicity coefficient $\alpha$, we consider a term related to the cross helicity, which represents the effect of the inhomogeneous mean flow, in the turbulent electromotive force. Second, this transport coefficient ($\gamma$) is not treated as an adjustable parameter, but the evolution equation for $\gamma$ is simultaneously solved. The basic scenario for the solar activity cycle in this approach is as follows: The toroidal field is induced by the toroidal rotation in mediation by the turbulent cross helicity. Then due to the $\alpha$ or helicity effect, the poloidal field is generated from the toroidal field. The poloidal field induced by the $\alpha$ effect produces a turbulent cross helicity whose sign is opposite to the original one (negative cross-helicity production). The cross helicity with this opposite sign induces a reversed toroidal field. Results of the eigenvalue analysis of the model equations are shown, which confirm the above scenario.