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

TL;DR

This paper develops mean-field solar dynamo models with deep-seated meridional circulation, showing they can replicate some aspects of the solar magnetic cycle, but also reveal discrepancies needing further helioseismic investigation.

Contribution

It introduces kinematic dynamo models with a specific meridional flow pattern that produce sunspot-like magnetic activity, highlighting the importance of circulation structure for solar cycle modeling.

Findings

Toroidal magnetic field concentrates at the convection zone bottom.

Cycle period does not always decrease with faster meridional flow.

Phase relations between magnetic components show discrepancies with observations.

Abstract

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.