Prediction of the Solar Polar Fields in 2026: An Unusually Weak Level Across the Last Five Solar Cycles

TL;DR

This paper predicts that the solar polar fields in 2026 will be unusually weak across solar cycle 25, using surface flux-transport models validated with recent data and a new meridional flow profile.

Contribution

The study introduces a validated prediction method for solar polar fields in cycle 25 using a newly constrained meridional flow profile and recent magnetogram data.

Findings

Southern polar field is predicted to strengthen gradually.

Northern polar field is expected to decline sharply until March 2026.

Northern polar field may become exceptionally weak at cycle minimum.

Abstract

Solar polar fields are essential for the solar cycle and the heliospheric magnetic field. Cycle 25 is now entering its declining phase, the critical period during which most of the cycle's polar fields are established. Therefore, reliable polar-field prediction is now especially important. Polar-field evolution is governed by the poleward transport of already-emerged active-region (AR) flux over a timescale of a few years. Thus, surface flux-transport models can reliably provide one-year predictions without requiring information about future AR emergence. Our prediction method is validated using simulations of the surface magnetic field from 2020-2025 and hindcasts of the 2023-2024 polar fields, employing a newly constrained profile of the meridional flow. Using the most recent HMI synoptic magnetogram as the initial condition, we predict the polar-field evolution from October 2025 to October 2026. The southern polar field is predicted to strengthen gradually, while the northern field is expected to decline sharply until March 2026 due to some ARs with abnormal polarity. By that time, the northern polar field becomes exceptionally weak, and the southern field remains relatively weak, raising concerns about the polar-field strength at the cycle 25/26 minimum and the amplitude of cycle 26.