Presentation #110.02 in the session General Topics II — Solar.
The strength of the polar fields and the strength of the geomagnetic precursors (e.g., the aa index) at solar minimum are both well established as predictors of the amplitude of the following cycle. Surface Flux Transport (SFT) models describe the process in which the near surface flows transport magnetic flux from the active region belts to the poles and can be used to estimate the polar field strength well before minimum. The Advective Flux Transport (AFT) model, a state-of-the-art SFT model, was designed with the intent of creating the most realistic SFT model possible by incorporating the observed active regions and surface flows directly, with minimal parameterizations. AFT has proven successful at predicting active region evolution and decay as well as the evolution of the Sun’s polar fields several years in advance. In 2016 and 2018, AFT was used to create forecasts of the Sun’s polar field in order to predict the strength of Solar Cycle 25 - predicting a weak cycle. During solar minimum (December 2019) the polar field precursor and the geomagnetic precursor both indicated that Cycle 25 would indeed be a small cycle, but the prediction from the geomagnetic precursor was about 20-30% higher than the prediction from the polar fields. Now that we are a couple of years into the cycle, we can also use curve fitting to provide an additional prediction for the amplitude of Solar Cycle 25. We will present an update on the current state of solar cycle activity and show how the latest observations of the polar fields and the solar cycle strength compare with the AFT predictions. We will show a comparison of the prediction from the geomagnetic and polar field precursor methods. Finally, we will provide an update on the outlook for Solar Cycle 25 based on the curve fitting method and how this compares to the predictions from the precursor methods.