Timing Terminators: Forecasting Sunspot Cycle 25 Onset and Activity Levels (Invited Presentation)

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 takes place in the solar interior. 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 this technique we can achieve higher fidelity terminator timing than previous estimates have permitted. Further, this method presents a unique opportunity to project when the next terminator will occur, 2020.33 (±0.16), and trigger the growth of sunspot cycle 25. (This is earlier than flux transport dynamo-type predictions.) We further predict Cycle 25's sunspot number will be of similar magnitude to Cycle 24 (so we are not heading to a grand minimum, but still relatively weak by historical standards), but of course the sunspot max and (Space Weather) activity max are rarely one and the same.

We also will use the Hilbert method to show why Cycle 23 was unusually long, why the Cycle 23-24 minimum in 2007--2009 was unusually quiet, and why neither of these occurrences will happen with the end of Cycle 24 in 2020.