Dynamo saturation through the latitudinal variation of bipolar magnetic regions in the Sun

TL;DR

This paper proposes a mechanism within the Babcock--Leighton dynamo framework where the latitudinal variation of bipolar magnetic regions (BMRs) at higher latitudes in stronger solar cycles limits the growth of the Sun's magnetic field, explaining cycle saturation.

Contribution

It introduces a 3D Babcock--Leighton dynamo model demonstrating how latitudinal BMR variation can naturally limit magnetic field amplification in the Sun.

Findings

Higher latitude BMRs produce less poloidal field.

The model reproduces observed cycle saturation.

Latitudinal variation acts as a self-regulating mechanism.

Abstract

Observations of the solar magnetic cycle showed that the amplitude of the cycle did not grow all the time in the past. Thus, there must be a mechanism to halt the growth of the magnetic field in the Sun. We demonstrate a recently proposed mechanism for this under the Babcock--Leighton dynamo framework, which is believed to be the most promising paradigm for the generation of the solar magnetic field at present. This mechanism is based on the observational fact that the stronger solar cycles produce bipolar magnetic regions (BMRs) at higher latitudes and thus have higher mean latitudes than the weaker ones. We capture this effect in our three-dimensional Babcock--Leighton solar dynamo model and show that when the toroidal magnetic field tries to grow, it produces BMRs at higher latitudes. The BMRs at higher latitudes generate a less poloidal field, which consequently limits the overall growth of the magnetic field in our model. Thus, our study suggests that the latitudinal variation of BMRs is a potential mechanism for limiting the magnetic field growth in the Sun.