Nonlinear mechanisms that regulate the solar cycle amplitude

Abstract

The solar magnetic activity cycle has an amplitude that varies within a wide but limited range of values. This implies that there are non-linear mechanisms that prevent runaway solutions. The purpose of this paper is to propose observable non-linear mechanisms in the framework of the Babcock-Leighton-type dynamo. Sunspot emergences show systematic properties that strong cycles tend to have higher mean latitudes and lower tilt angle coefficients. We use the surface flux transport model to investigate the effect of these systematic properties on the expected final total dipolar moment, i.e. cancellation plus generation of dipole moment by a whole solar cycle. We demonstrate that the systematic change in latitude has similar nonlinear feedback on the solar cycle (latitudinal quenching) as tilt does (tilt quenching). Both forms of quenching lead to the expected final total dipolar moment being enhanced for weak cycles and being saturated to a nearly constant value for normal and strong cycles. This explains observed long-term solar cycle variability, e.g., the Gnevyshev-Ohl rule, which, in turn, justifies the non-linear mechanisms inherent in the Babcock-Leighton-type dynamo.

The polar precursor method for solar cycle prediction: comparison of predictors and their temporal range

“…We note that recently some evidence of nonlinear quenching in the tilt is observed in the BMR data (Jha et al 2020). As shown in Jiang (2020) and Karak (2020), the observed latitude variation of BMRs provides another nonlinearity to stabilize the magnetic cycles in Babcock-Leighton dynamos. In addition to the tilt quenching, this nonlinearity is also operating in the model to limit the amplitudes of the magnetic cycles.…”

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

“…We have demonstrated the saturation of the magnetic field in the kinematic Babcock-Leighton type flux transport dynamo models through the latitudinal quenching as proposed by Jiang (2020). It is based on the observed fact that the stronger cycles produce sunspots and BMRs at higher latitudes than the weaker ones.…”

“…We note that in our modeled solar cycle, we do not observe the Gnevyshev-Ohl rule even when we include the tilt quenching in addition to the latitude quenching. Hence, the prediction of Jiang (2020) based on the SFT model does not hold in our dynamo model.…”

“…Another possible mechanism for limiting the growth of the magnetic field in Sun, as highlighted by Jiang (2020), can be the following. It is observed that the stronger cycles start producing BMRs at higher latitudes and thus have higher mean latitudes than the weaker ones (Waldmeier 1955;Solanki et al 2008;Jiang et al 2011;Mandal et al 2017).…”

“…The BMRs at higher latitudes are far less efficient in producing a poloidal field than those at lower latitudes (Jiang et al 2014). On computing the total axial dipole moment at the end of the cycle in an SFT model, Jiang (2020) showed that this effect acts as a quenching in the growth of the dipole moment and thus helps to regulate the solar cycle amplitude. She calls this as the latitudinal quenching.…”