Why does the Sun's torsional oscillation begin before the sunspot cycle?

TL;DR

This paper offers a theoretical explanation for why the Sun's torsional oscillation starts before the sunspot cycle, using a solar dynamo model with specific meridional circulation characteristics.

Contribution

It introduces a solar dynamo model with deep meridional circulation that explains the early onset of torsional oscillations prior to sunspot cycle appearance.

Findings

Torsional oscillation begins 2-3 years before sunspots.

Deep meridional circulation influences early toroidal field formation.

Model predicts high-latitude toroidal field emergence.

Abstract

Although the Sun's torsional oscillation is believed to be driven by the Lorentz force associated with the sunspot cycle, this oscillation begins 2--3 yr before the sunspot cycle. We provide a theoretical explanation of this with the help of a solar dynamo model having a meridional circulation penetrating slightly below the bottom of the convection zone, because only in such dynamo models the strong toroidal field forms a few years before the sunspot cycle and at a higher latitude.