Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude

Scott W Mcintosh,Ricky Egeland,Nicholas W Watkins,Sandra Chapman,Robert J Leamon

doi:10.1007/s11207-020-01723-y

Abstract

The Sun exhibits a well-observed modulation in the number of spots on its disk over a period of about 11 years. From the dawn of modern observational astronomy, sunspots have presented a challenge to understanding—their quasi-periodic variation in number, first noted 175 years ago, has stimulated community-wide interest to this day. A large number of techniques are able to explain the temporal landmarks, (geometric) shape, and amplitude of sunspot “cycles,” however, forecasting these features accurately in advance remains elusive. Recent observationally-motivated studies have illustrated a relationship between the Sun’s 22-year (Hale) magnetic cycle and the production of the sunspot cycle landmarks and patterns, but not the amplitude of the sunspot cycle. Using (discrete) Hilbert transforms on more than 270 years of (monthly) sunspot numbers we robustly identify the so-called “termination” events that mark the end of the previous 11-yr sunspot cycle, the enhancement/acceleration of the present cycle, and the end of 22-yr magnetic activity cycles. Using these we extract a relationship between the temporal spacing of terminators and the magnitude of sunspot cycles. Given this relationship and our prediction of a terminator event in 2020, we deduce that sunspot Solar Cycle 25 could have a magnitude that rivals the top few since records began. This outcome would be in stark contrast to the community consensus estimate of sunspot Solar Cycle 25 magnitude.

Highlights

The ebb and flow in the number of dark spots on the solar disk has motivated literally thousands of investigations since the discovery of the eponymous quasi-periodic 11-year sunspot cycle by (Schwabe, 1844, Figure 1)
Sunspot cycle prediction is a high-stakes business and has become a decadal event, starting officially for Solar Cycle (Joselyn et al, 1997), and repeated for Solar Cycle (Pesnell, 2008), the effort brought together a range of subject matter experts and an array of submitted methods that range from polar magnetic field precursors, through numerical models, and using observed climatologies to extrapolate in time (e.g. Petrovay, 2020)
The phenomenological model presented in M2014, and employed above, differs in one critical regard from the conventional physics-based models employed in the SC25PP, similar recently published efforts (Bhowmik and Nandy, 2018), and for machine-learninginspired models (Kitiashvili, 2020)

Summary

Introduction

The (decadal) ebb and flow (waxing and waning) in the number of dark spots on the solar disk has motivated literally thousands of investigations since the discovery of the eponymous quasi-periodic 11-year sunspot cycle by (Schwabe, 1844, Figure 1). Charbonneau, 2010, 2014; Brun et al, 2015; Cameron, Dikpati, and Brandenburg, 2017) in addition to numerically forecasting the properties of upcoming cycles using statistical (e.g. Pesnell, 2018; Pesnell and Schatten, 2018) or physical methods Sunspot cycle prediction is a high-stakes business and has become a decadal event, starting officially for Solar Cycle (Joselyn et al, 1997), and repeated for Solar Cycle (Pesnell, 2008), the effort brought together a range of subject matter experts and an array of submitted methods that range from polar magnetic field precursors, through numerical models, and using observed climatologies to extrapolate in time (e.g. Petrovay, 2020). It is worth noting that the ‘polar field precursor’ method, which uses measurements of the Sun’s polar magnetic field at solar minimum to predict the upcoming sunspot cycle strength, proved to be accurate for Solar Cycle 24 (e.g. Svalgaard, Cliver, and Kamide, 2005; Schatten, 2005) and has informed much of the science that has followed

Results

Discussion

Conclusion