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SPACE SCIENCE

The 'Termination Event' has arrived

By Dr Tony Phillips, Spaceweather.com

A ‘Termination Event’ is a controversial new way of predicting how strong the next solar cycle
will be. Cycle 25 will be above average.

n 25 February 2022 something
big happened on the sun. Solar
Ophysicists Scott McIntosh (NCAR)
and Bob Leamon (U. Maryland-Baltimore)
call it ‘the Termination Event.’ “Old Solar
Cycle 24 has finally died–it was terminated!”
says McIntosh. “Now the new solar cycle,
Solar Cycle 25, can really take off.”
The ‘Termination Event’ is a new idea
in solar physics, outlined by McIntosh and
Leamon in a December 2020 paper in the
journal Solar Physics. Not everyone accepts
it – yet. If Solar Cycle 25 unfolds as McIntosh
and Leamon predict, the ‘Termination
Event’ will have to be taken seriously.
The basic idea is this: Solar Cycle 25 Predictions for Solar Cycle 25. Green would be average. Blue is the ‘official’ prediction of a weak cycle.
(SC25) started in December 2019. However, Red is a 2020 prediction based on the ‘termination event.’
old Solar Cycle 24 (SC24) refused to go away.
It hung on for two more years, producing “We found that the longer the time between terminators, the weaker the next cycle would
occasional old-cycle sunspots and clogging be,” explains Leamon. “Conversely, the shorter the time between terminators, the stronger the
the sun’s upper layers with its decaying next solar cycle would be.”
magnetic field. During this time, the two So when did the latest ‘termination event’ happen? It was December 2021, two years after
cycles coexisted, SC25 struggling to break Solar Cycle 25 began. This results in a specific testable prediction for Solar Cycle 25.
free while old SC24 held it back. “We have finalised our forecast of SC25’s amplitude,” says McIntosh. “It will be just above
“Solar Cycle 24 was cramping Solar the historical average with a monthly smoothed sunspot number of 190 ± 20.”
Cycle 25’s style,” says Leamon. ‘Above average’ may not sound exciting, but this is in fact a sharp departure from NOAA’s
Researchers have long known that solar official forecast of a weak solar cycle. It could be just enough to catapult terminators into the
cycles can overlap. This is nothing new. The forefront of solar cycle prediction techniques. n
twist added by McIntosh and Leamon is that
overlapping cycles can interact. It makes
sense. In the early 20th century, George
Ellery Hale discovered that the magnetic
polarity of sunspot pairs reverses itself from
one cycle to the next; indeed, the sun’s entire
global magnetic field flips every ~11 years.
When adjacent, opposite polarity solar cycles
overlap and they naturally interfere.
Termination events mark the end of the
overlap period, when a new cycle can break
free of the old.
Moreover, the timing of the ‘termination
event’ can predict the intensity of the new
cycle. In their Solar Physics paper, McIntosh
and Leamon looked back over 270 years of
sunspot data and found that ‘termination Bands of coronal bright points (hot spots in the sun’s atmosphere) linked to old Solar Cycle 24 vanished in
events’ happen every 10 to 15 years. December 2021, signalling a termination event.

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