An overshoot solar dynamo with a strong return meridional flow

TL;DR

This paper presents a flux-transport solar dynamo model with strong return meridional flow and a deep stagnation point, demonstrating consistency with observed solar activity cycles and revealing new insights into dipolar and quadrupolar solution thresholds.

Contribution

It introduces a linear dynamo model with a positive α-effect in the overshoot layer and a deep stagnation point, showing improved agreement with solar observations and novel findings on dynamo solution thresholds.

Findings

Migration of toroidal belts matches observed solar patterns

Cycle periods are consistent with solar activity cycles

Dipolar solutions have lower critical dynamo numbers than quadrupolar solutions

Abstract

The meridional circulation plays an essential role in determining the basic mechanism of the dynamo action in case the of a low eddy diffusivity. Flux-transport dynamos with strong return flow and a deep stagnation point are discussed in the case of a positive $\alpha$-effect located in the overshoot layer and a rotation law consistent with helioseismology. By means of a linear dynamo model, it will be shown that the migration of the toroidal belts at lower latitudes and the periods of the activity cycles are consistent with the observations. Moreover, at variance with previous investigations, the typical critical dynamo numbers of dipolar solutions are significantly smaller that those of quadrupolar solutions even in the regime of strong flow.