Helicity-vorticity turbulent pumping of magnetic fields in solar convection zone

We study the effect of turbulent drift of a large-scale magnetic field that results from the interaction of helical convective motions and differential rotation in the solar convection zone. The principal direction of the drift corresponds to the direction of the large-scale vorticity vector. Thus, the effect produces a latitudinal transport of the large-scale magnetic field in the convective zone wherever the angular velocity has a strong radial gradient. The direction of the drift depends on the sign of helicity and it is defined by the Parker-Yoshimura rule. The analytic calculations are done within the framework of mean-field magnetohydrodynamics using the minimal \tau-approximation. We estimate the magnitude of the drift velocity and find that it can be several m/s near the base of the solar convection zone. The implications of this effect for the solar dynamo are illustrated on the basis of an axisymmetric mean-field dynamo model with a subsurface shear layer. We find that the helicity--vorticity pumping effect can have an influence on the features of the sunspot time--latitude diagram, producing a fast drift of the sunspot activity maximum at the rise phase of the cycle and a slow drift at the decay phase of the cycle.Comment: 19 pages, 8 figures, submitted to GAF

Mean-field solar dynamo models with strong meridional flow at the bottom of the convection zone

The paper presents a study of kinematic axisymmetric mean-field dynamo models for a case of the meridional circulation with a deep-seated stagnation point and a strong return flow at the bottom of the convection zone. This kind of circulation follows from mean-field models of the angular momentum balance in the solar convection zone. We show that it is possible for this types of meridional circulation to construct kinematic dynamo models that resemble in some aspects the sunspot magnetic activity cycle. The dynamo model includes turbulent sources of the large-scale poloidal magnetic field production, due to kinetic helicity and a combined effect due to Coriolis force and the large-scale current. In these models the toroidal magnetic field, which is responsible for the sunspot production, is concentrated at the bottom of the convection zone, and is transported to low-latitude regions by the meridional flow. The meridional component of the poloidal field is also concentrated at the bottom of the convection zone while the radial component is concentrated in near polar regions. There are some issues which, perhaps, are resulted from the given meridional circulation pattern and the distribution of the magnetic diffusivity inside convection zone. In particular, in the near-equatorial regions the phase relations between the toroidal and poloidal components disagree with observations. Also, we show that the period of the magnetic cycle may not always monotonically decrease with the increase of the meridional flow speed. Thus, for the further progress it is important to determine the structure of the meridional circulation, which is one of the critical properties, from helioseismology observations

On the origin of the double cell meridional circulation in the solar convection zone

Recent advances in helioseismology, numerical simulations and mean-field theory of solar differential rotation have shown that the meridional circulation pattern may consist of two or more cells in each hemisphere of the convection zone. According to the mean-field theory the double-cell circulation pattern can result from the sign inversion of a nondiffusive part of the radial angular momentum transport (the so-called $\Lambda$-effect) in the lower part of the solar convection zone. Here, we show that this phenomenon {can result} from the radial inhomogeneity of the Coriolis number, which depends on the convective turnover time. We demonstrate that if this effect is taken into account then the solar-like differential rotation and the double-cell meridional circulation are both reproduced by the mean-field model. The model is consistent with the distribution of turbulent velocity correlations determined from observations by tracing motions of sunspots and large-scale magnetic fields, indicating that these tracers are rooted just below the shear layer.Comment: 22 pages, 6 figures, accepted in Ap

Advances in mean-field dynamo theories

We give a short introduction to the subject and review advances in understanding the basic ingredients of the mean-field dynamo theory. The discussion includes the recent analytic and numerical work in developments for the mean electromotive force of the turbulent flows and magnetic field, the nonlinear effects of the magnetic helicity, the non-local generation effects in the dynamo. We give an example of the mean-field solar dynamo model that incorporates the fairly complete expressions for the mean-electromotive force, the subsurface shear layer and the conservation of the total helicity. The model is used to shed light on the issues in the solar dynamo and on the future development of this field of research.Comment: Revision2, replaced two figures by color version, 12 pages, IAU 294 Proceeding