Towards an algebraic method of solar cycle prediction

Melinda Nagy,Paul Charbonneau,Kristóf Petrovay,Alexandre Lemerle

doi:10.1051/swsc/2020051

Abstract

An algebraic method for the reconstruction and potentially prediction of the solar dipole moment value at sunspot minimum (known to be a good predictor of the amplitude of the next solar cycle) was suggested in the first paper in this series. The method sums up the ultimate dipole moment contributions of individual active regions in a solar cycle: for this, detailed and reliable input data would in principle be needed for thousands of active regions in a solar cycle. To reduce the need for detailed input data, here we propose a new active region descriptor called ARDoR (Active Region Degree of Rogueness). In a detailed statistical analysis of a large number of activity cycles simulated with the 2 × 2D dynamo model we demonstrate that ranking active regions by decreasing ARDoR, for a good reproduction of the solar dipole moment at the end of the cycle it is sufficient to consider the top N regions on this list explicitly, where N is a relatively low number, while for the other regions the ARDoR value may be set to zero. For example, with N = 5 the fraction of cycles where the dipole moment is reproduced with an error exceeding ±30% is only 12%, significantly reduced with respect to the case N = 0, i.e. ARDoR set to zero for all active regions, where this fraction is 26%. This indicates that stochastic effects on the intercycle variations of solar activity are dominated by the effect of a low number of large “rogue” active regions, rather than the combined effect of numerous small ARs. The method has a potential for future use in solar cycle prediction.

Highlights

An algebraic method for the reconstruction and potentially prediction of the solar dipole moment value at sunspot minimum was suggested in the first paper in this series
In each solar cycle thousands of active regions are listed in the official NOAA database and many more small active regions are missed if their heliographic position and lifetime do not render them directly observable on the visible hemisphere
As demonstrated in Paper 1, f1 is in turn given by 1 dk = d sina where d is the full angular polarity separation on the solar surface and a is the tilt angle of the bipole axis relative to the east–west direction, the sign of a being negative for bipoles disobeying Hale’s polarity rules. It was numerically demonstrated in Paper 1 that this Gaussian form holds quite generally irrespective of the details of the surface magnetic flux transport (SFT) model, its parameters only have a very weak dependence on the assumed form of the meridional flow profile, and their value only depends on a single combination of SFT model parameters

Summary

Reducing the need for detailed input data with ARDoR

Abstract – An algebraic method for the reconstruction and potentially prediction of the solar dipole moment value at sunspot minimum (known to be a good predictor of the amplitude of the solar cycle) was suggested in the first paper in this series. With N = 5 the fraction of cycles where the dipole moment is reproduced with an error exceeding ±30% is only 12%, significantly reduced with respect to the case N = 0, i.e. ARDoR set to zero for all active regions, where this fraction is 26%. This indicates that stochastic effects on the intercycle variations of solar activity are dominated by the effect of a low number of large “rogue” active regions, rather than the combined effect of numerous small ARs. The method has a potential for future use in solar cycle prediction

General introduction

Introducing ARDoR

ARDoR and rogue active regions in the 2 Â 2D dynamo model

Findings

Conclusions