Predicting the Amplitude and Hemispheric Asymmetry of Solar Cycle 25 with Surface Flux Transport

TL;DR

This study uses surface flux transport simulations constrained by observations to predict the amplitude and hemispheric asymmetry of Solar Cycle 25, highlighting the uncertainties and limitations in long-term solar cycle forecasting.

Contribution

The paper introduces a flux transport modeling approach with observational constraints to predict Solar Cycle 25's strength and asymmetry, accounting for stochastic uncertainties.

Findings

Cycle 25 will likely be similar in strength to Cycle 24.

Hemispheric asymmetry favors stronger southern polar fields.

Uncertainty in predictions is approximately 15% due to stochastic variations.

Abstract

Evidence strongly indicates that the strength of the Sun's polar fields near the time of a sunspot cycle minimum determines the strength of the following solar activity cycle. We use our Advective Flux Transport (AFT) code, with flows well constrained by observations, to simulate the evolution of the Sun's polar magnetic fields from early 2016 to the end of 2019 --- near the expected time of Cycle 24/25 minimum. We run a series of simulations in which the uncertain conditions (convective motion details, active region tilt, and meridional flow profile) are varied within expected ranges. We find that the average strength of the polar fields near the end of Cycle 24 will be similar to that measured near the end of Cycle 23, indicating that Cycle 25 will be similar in strength to the current cycle. In all cases the polar fields are asymmetric with fields in the south stronger than those in the north. This asymmetry would be more pronounced if not for the predicted weakening of the southern polar fields in late 2016 and through 2017. After just four years of simulation the variability across our ensemble indicates an accumulated uncertainty of about 15\%. This accumulated uncertainty arises from stochastic variations in the convective motion details, the active region tilt, and changes in the meridional flow profile. These variations limit the ultimate predictability of the solar cycle.