Timing Terminators: Forecasting Sunspot Cycle 25 Onset

TL;DR

This paper introduces a signal processing method using the Hilbert transform to identify solar terminators in sunspot data, enabling more accurate timing and forecasting of sunspot cycle 25's onset.

Contribution

The study applies the Hilbert transform to sunspot and radio flux data to precisely identify terminators and predict the start of solar cycle 25.

Findings

Identified a robust signature of terminators in sunspot records.

Projected the next terminator to occur around May 2020.

Enhanced the accuracy of solar cycle timing estimates.

Abstract

Recent research has demonstrated the existence of a new type of solar event, the "terminator." Unlike the Sun's signature events, flares and Coronal Mass Ejections, the terminator most likely originates in the solar interior, at or near the tachocline. The terminator signals the end of a magnetic activity cycle at the Sun's equator and the start of a sunspot cycle at mid latitudes. Observations indicate that the time difference between these events is very short, less than a solar rotation, in the context of the sunspot cycle. As the (definitive) start and end point of solar activity cycles the precise timing of terminators should permit new investigations into the meteorology of our star's atmosphere. In this letter we use a standard method in signal processing, the Hilbert transform, to identify a mathematically robust signature of terminators in sunspot records and in radiative proxies. Using a linear extrapolation of the Hilbert phase of the sunspot number and F10.7 solar radio flux time series we can achieve higher fidelity historical terminator timing than previous estimates have permitted. Further, this method presents a unique opportunity to project, from analysis of sunspot data, when the next terminator will occur, May 2020 ($+4$, $-1.5$ months), and trigger the growth of sunspot cycle 25.