Predicting the Timing of the the Solar Cycle 25 Polar Field Reversal

TL;DR

This study targets forecasting the timing of Solar Cycle 25 polar-field reversals using the Advective Flux Transport (AFT) model in predictive mode, driven by ensembles of synthetic active regions generated by SARG based on Cycle 13. The Baseline map from magnetograms through 2023-08-31 serves as the initial condition, after which 30 SARG realizations are propagated to 2027 to estimate reversal times and associated uncertainties via two independent methods. The Northern hemisphere is predicted to reverse around August 2024 (June–November 2024), and the Southern around February 2025 (November 2024–July 2025), with a consistent ~5-month hemispheric lag and a mid-2024 axial dipole moment reversal. The approach demonstrates a practical workflow for solar-cycle prediction with quantified uncertainty, highlighting the role of stochastic active-region emergence in limiting long-term forecasts and enabling validation against upcoming reversals.

Abstract

The process of the Sun's polar field cancellation reversal commences with the emergence of new cycle Hale's polarity active regions. Once the Sun undergoes polarity reversal, typically occurring near the peak of solar activity, it begins the process of accumulating the seed field for the forthcoming solar cycle. In recent years, the Advective Flux Transport (AFT) model has proven highly effective in forecasting the progression of polar fields by leveraging observations of surface flows and magnetic flux emergence. In this study, we make use of the predictive capability of the AFT model to simulate the evolution of the polar fields and estimate the timing of the Solar Cycle 25 polarity reversal in both hemispheres of the Sun. We use the statistical properties of active regions along with Solar Cycle~13, which closely resembles the current solar cycle (Cycle~25), to generate synthetic active regions in order to simulate future magnetic flux emergence in AFT to predict the evolution of the polar field. Based on our simulations, we anticipate that the Northern hemisphere of the Sun will undergo a polarity reversal between June 2024 and November 2024, with the center of our distribution at August 2024. In the Southern hemisphere, we anticipate a polarity reversal between November 2024 and July 2025, centered around February 2025. Additionally, assuming that the reversal of the axial dipole moment coincides with the peak of the solar cycle, our findings indicate that Cycle 25 is expected to peak in 2024 (likely between April to August 2024).

Figures (4)

• Figure 1: (a) The monthly average sunspot number for current cycle (Cycle 25), along with monthly average sunspot number for Cycle 13 and the best fit curve based on Hathaway1994. (b) shows the time latitude butterfly diagram for Cycle 25 up to August 2023 and one SARG realizations of synthetic ARs from September 2023 onward.
• Figure 2: The magnetic butterfly diagram, constructed using AFT Baseline map till 31st August 2023 (marked using white dashed vertical line) and after that using one of the realizations of synthetic ARs in AFT's predictive mode.
• Figure 3: The polar field above $60\hbox{$^\circ$}$ latitude for the (a) Northern and (b) Southern hemispheres is shown from the AFT Baseline through August 2023 (solid line), and for 30 SARG realizations afterward (light color lines). For reference, the HMI polar field above $60\hbox{$^\circ$}$ is also shown (light gray). The median of the 30 realizations is indicated by the solid line after August 2023. The median polar field measurements for the Northern (c) and Southern (d) hemisphere are shown in the same manner. Here, the shaded color regions represent the 50% confidence interval between the first (Q1) and third (Q3) quartiles. The timing of the polar field reversal is marked by the vertical lines with the corresponding months noted in the legend.
• Figure 4: The violin plot shows the median timing of the polar field reversal, along with other statistical parameters such as the first (Q1) and third (Q3) quartiles, and the median timing of the reversal in the Northern (red) and Southern (blue) hemispheres. The third violin (brown) represents the distribution for the reversal of the axial dipole moment.