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Abstract:
The strength of the polar fields and the geomagnetic precursors (e.g., the aa index) at solar minimum are established predictors of the amplitude of the solar cycle. Surface Flux Transport (SFT) models describe the process by which magnetic flux from the active regions is transported 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. AFT has proven successful at predicting active region evolution and decay as well as the evolution of the Sun’s polar fields. In 2016 and 2018, AFT was used to create forecasts of the Sun's polar field and predict the strength of Solar Cycle 25 - predicting a weak cycle. During solar minimum (December 2019) the polar field and geomagnetic precursors 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 well into the cycle, we can use curve fitting to provide an additional prediction for the amplitude of Solar Cycle 25. We present an update on the current state of the solar cycle and show how the latest observation compare with the AFT predictions. We show a comparison of the prediction from the geomagnetic and polar field precursor methods. Finally, we provide an update on the outlook for Solar Cycle 25.
