Solar-cycle precursors and predictions

TL;DR

This paper reviews solar cycle precursors, especially polar fields and geomagnetic indices, discusses their predictive capabilities, explores underlying physical mechanisms, and highlights the limitations due to nonlinearities and randomness in sunspot emergence.

Contribution

It provides a comprehensive analysis of solar cycle precursors, examines the physical mechanisms behind them, and proposes a dynamo-based model for improved solar cycle prediction.

Findings

Polar field has high predictive skill for solar cycle amplitude.

Radial downward pumping may explain short magnetic memory.

No correlation exists between polar field and previous cycle strength.

Abstract

The sunspot number data during the past 400 years indicates that both the profile and the amplitude of the solar cycle have large variations. Some precursors of the solar cycle were identified aiming to predict the solar cycle. The polar field and the geomagnetic index are two precursors which are received the most attention. The geomagnetic variations during the solar minima are potentially caused by the solar polar field by the connection of the solar open flux. The robust prediction skill of the polar field indicates that the memory of the dynamo process is less than 11 yrs within the framework of the Babcock-Leighton flux transport dynamo. One possible reason to get the short magnetic memory is the high magnetic diffusivity in the convective zone. Our recent studies show that the radial downward pumping is another possible reason. Based upon the mechanism, we well simulate the cycle irregularities during RGO time period. This opens the possibility to set up a standard dynamo based model to predict the solar cycle. In the end, the no correlation between the polar field and the preceding cycle strength due to the nonlinearities and random mechanisms involved in the sunspot emergences are stressed.