Solar Cycle Propagation, Memory, and Prediction: Insights from a Century of Magnetic Proxies

TL;DR

This study uses a century of magnetic proxies to analyze solar cycle propagation, memory, and prediction, highlighting the importance of polar fields and tilt in cycle amplitude forecasting.

Contribution

It demonstrates that combining sunspot area with tilt improves cycle prediction and provides evidence that solar cycle memory is limited to one cycle.

Findings

Polar magnetic fields are reliable predictors of cycle amplitude.

Sunspot area alone is uncorrelated with cycle strength.

Cycle memory is limited to only one cycle.

Abstract

The solar cycle and its associated magnetic activity are the main drivers behind changes in the interplanetary environment and the Earth's upper atmosphere (commonly referred to as space weather). These changes have a direct impact on the lifetime of space-based assets and can create hazards to astronauts in space. In recent years there has been an effort to develop accurate solar cycle predictions (with aims at predicting the long-term evolution of space weather), leading to nearly a hundred widely spread predictions for the amplitude of solar cycle 24. A major contributor to the disagreement is the lack of direct long-term databases covering different components of the solar magnetic field (toroidal vs.\ poloidal). Here we use sunspot area and polar faculae measurements spanning a full century (as our toroidal and poloidal field proxies), to study solar cycle propagation, memory, and prediction. Our results substantiate predictions based on the polar magnetic fields, whereas we find sunspot area to be uncorrelated to cycle amplitude unless multiplied by area-weighted average tilt. This suggests that the joint assimilation of tilt and sunspot area is a better choice (with aims to cycle prediction) than sunspot area alone, and adds to the evidence in favor of active region emergence and decay as the main mechanism of poloidal field generation (i.e. the Babcock-Leighton mechanism). Finally, by looking at the correlation between our poloidal and toroidal proxies across multiple cycles, we find solar cycle memory to be limited to only one cycle.