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

TL;DR

This paper introduces a novel method using Hilbert transforms to analyze magnetic activity cycles and predict the amplitude of Sunspot Cycle 25, suggesting it may be among the strongest on record, contrary to current estimates.

Contribution

It identifies and utilizes terminator events to relate magnetic cycle timing to sunspot cycle amplitude, providing a new predictive approach for solar activity.

Findings

Predicted Sunspot Cycle 25 to be among the strongest since records began.

Identified a relationship between terminator event timing and cycle magnitude.

Forecasted a 2020 terminator event influencing cycle amplitude prediction.

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, stimulates 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 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 cycle 25 magnitude.