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Nonkinematic solar dynamo models with double-cell meridional circulation  

Valery Pipin   Submitted: 2018-08-06 19:51

Employing the standard solar interior model as input we construct a dynamically-consistent nonlinear dynamo model that takes into account the detailed description of the - effect, turbulent pumping, magnetic helicity balance, and magnetic feedback on the differential rotation and meridional circulation. The background mean-field hydrodynamic model of the solar convection zone accounts the solar-like angular velocity profile and the double-cell meridional circulation. We investigate an impact of the nonlinear magnetic field generation effects on the long-term variability and properties of the magnetic cycle. The nonlinear dynamo solutions are studied in the wide interval of the α effect parameter from a slightly subcritical to supercritical values. It is found that the magnetic cycle period decreases with the increasing cycle's magnitude. The periodic long-term variations of the magnetic cycle are excited in case of the overcritical α effect. These variations result from the hemispheric magnetic helicity exchange. It depends on the magnetic diffusivity parameter and the magnetic helicity production rate. The large-scale magnetic activity modifies the distribution of the differential rotation and meridional circulation inside convection zone. It is found that the magnetic feedback on the global flow affects the properties of the long-term magnetic cycles. We confront our findings with solar and stellar magnetic activity observations.

Authors: V.V. Pipin
Projects: None

Publication Status: JASTP (online)
Last Modified: 2018-08-08 11:37
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On the Origin of the Double-cell Meridional Circulation in the Solar Convection Zone  

Valery Pipin   Submitted: 2018-02-13 19:49

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 Λ-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.

Authors: V.V. Pipin and A.G. Kosovichev
Projects: None

Publication Status: ApJ (online)
Last Modified: 2018-02-14 11:41
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A new dynamo pattern revealed by the tilt angle of bipolar sunspot groups  

Valery Pipin   Submitted: 2013-04-16 10:48

We obtain the latitude-time distribution of the averaged tilt angle of solar bipoles. For large bipoles, which are mainly bipolar sunspot groups, the spatially averaged tilt angle is positive in the Northern solar hemisphere and negative in the Southern, with modest variations during course of the solar cycle. We consider the averaged tilt angle to be a tracer for a crucial element of the solar dynamo, i.e. the regeneration rate of poloidal large-scale magnetic field from toroidal. The value of the tilt obtained crudely corresponds to a regeneration factor corresponding to about 10% of r.m.s. velocity of solar convection. These results develop findings of Kosovichev and Stenflo (2012) concerning Joy's law, and agree with the usual expectations of solar dynamo theory. Quite surprisingly, we find a pronounced deviation from these properties for smaller bipoles, which are mainly solar ephemeral regions. They possess tilt angles of approximately the same absolute value, but of opposite sign compared to that of the large bipoles. Of course, the tilt data for small bipoles are less well determined than those for large bipoles; however they remain robust under various modifications of the data processing.

Authors: A.Tlatov, E.Illarionov, D.Sokoloff, V.Pipin
Projects: None

Publication Status: accepted in MNRAS
Last Modified: 2013-04-17 12:21
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Abstracts by Author
Nonkinematic solar dynamo models with double-cell meridional circulation
On the Origin of the Double-cell Meridional Circulation in the Solar Convection Zone
A new dynamo pattern revealed by the tilt angle of bipolar sunspot groups

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