Dynamo models of grand minima

Abstract

Abstract. Since a universally accepted dynamo model of grand minima does not exist at the present time, we concentrate on the physical processes which may be behind the grand minima. After summarizing the relevant observational data, we make the point that, while the usual sources of irregularities of solar cycles may be sufficient to cause a grand minimum, the solar dynamo has to operate somewhat differently from the normal to bring the Sun out of the grand minimum. We then consider three possible sources of irregularities in the solar dynamo: (i) nonlinear effects; (ii) fluctuations in the poloidal field generation process; (iii) fluctuations in the meridional circulation. We conclude that (i) is unlikely to be the cause behind grand minima, but a combination of (ii) and (iii) may cause them. If fluctuations make the poloidal field fall much below the average or make the meridional circulation significantly weaker, then the Sun may be pushed into a grand minimum.

Flux-transport and mean-field dynamo theories of solar cycles

“…We shall concentrate here only on the last mechanism which is being studied systematically within the last couple of years, making just a few brief remarks on the first two mechanisms. An earlier review by Choudhuri (2012) discusses all the three mechanisms. For a more complete discussion on the fluctuations in the Babcock-Leighton mechanism, see a still earlier review (Choudhuri 2011).…”