Effects of large-scale non-axisymmetric perturbations in the mean-field solar dynamo

Abstract

We explore a response of a non-linear non-axisymmetric mean-field solar dynamo model to shallow non-axisymmetric perturbations. After a relaxation period the amplitude of the non-axisymmetric field depends on the initial condition, helicity conservation, and the depth of perturbation. It is found that a perturbation which is anchored at r=0.9R has a profound effect on the dynamo process, producing a transient magnetic cycle of the axisymmetric magnetic field, if it is initiated at the growing phase of the cycle. The non-symmetric with respect to the equator perturbation results in a hemispheric asymmetry of the magnetic activity. The evolution of the axisymmetric and non-axisymmetric field depends on the turbulent magnetic Reynolds number R_m. In the range of R_m=10^{4-6} the evolution returns to the normal course in the next cycle, in which the non-axisymmetric field is generated due to a non-linear alpha-effect and magnetic buoyancy. In the stationary state the large-scale magnetic field demonstrates a phenomenon of "active longitudes" with cyclic 180 degree "flip-flop" changes of the large-scale magnetic field orientation. The flip-flop effect is known from observations of solar and stellar magnetic cycles. However this effect disappears in the model which includes the meridional circulation pattern determined by helioseismology. The rotation rate of the non-axisymmetric field components varies during the relaxation period, and carries important information about the dynamo process.

41 pages, 11 figures, revised version

References in corpus (6)

• Detection of Equatorward Meridional Flow and Evidence of Double-Cell Meridional Circulation inside the Sun
• The mean electro-motive force, current- and cross-helicity under the influence of rotation, magnetic field and shear
• Azimuthal dynamo wave in spherical shell convection
• Magnetic helicity effects in astrophysical and laboratory dynamos
• Dependence of magnetic cycle parameters on period of rotation in nonlinear solar-type dynamos
• Multiperiodicity, modulations and flip-flops in variable star light curves III. Carrier fit analysis of LQ Hya photometry for 1982-2014

Cited by in corpus (11)

• Solar large-scale magnetic field and cycle patterns in solar dynamo
• Application of Synoptic Magnetograms to Global Solar Activity Forecast
• Nonlinear regimes in mean-field full-sphere dynamo
• The mean tilt of sunspot bipolar regions: theory, simulations and comparison with observations
• Effects of Emerging Bipolar Magnetic Regions in Mean-field Dynamo Model of Solar Cycles 23 and 24
• Dependence of stellar magnetic activity cycles on rotational period in nonlinear solar-type dynamo
• Does nonaxisymmetric dynamo operate in the Sun?
• The magnetic helicity density patterns from non-axisymmetric solar dynamo
• Parametric instability in periodically perturbed dynamos
• Principle of Helical \& Nonhelical Dynamo and $\alpha$ effect in Field Structure model
• Magnetic helicity in non-axisymmetric mean-field solar dynamo