Feb. 26, 2022: Something big just happened on the sun. Solar physicists Scott McIntosh (NCAR) and Bob Leamon (U. Maryland-Baltimore County) 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 (SC25) started in Dec. 2019. However, old Solar Cycle 24 (SC24) refused to go away. It hung on for two more years, producing occasional old-cycle sunspots and clogging the sun’s upper layers with its decaying magnetic field.  During this time, the two cycles coexisted, SC25 struggling to break free while old SC24 held it back.

“Solar Cycle 24 was cramping Solar Cycle 25’s style,” says Leamon.

Researchers have long known that solar cycles can overlap. The twist added by McIntosh and Leamon is the realization that overlapping cycles interact. This 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, they naturally interfere.

Termination Events mark the end of interference, when a new cycle can break free of the old.

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 Events happen every 10 to 15 years.

“We found that the longer the time between terminators, the weaker the next cycle would be,” explains Leamon. “Conversely, the shorter the time between terminators, the stronger the next solar cycle would be.”

So when did the latest Termination Event happen? Dec. 2021. This yields a specific, testable prediction for Solar Cycle 25.

“We have finalized our forecast of SC25’s amplitude,” says McIntosh. “It will be just above the historical average with a monthly smoothed sunspot number of 190 ± 20.”

“Above average” may not sound exciting, but this is in fact a sharp departure from NOAA’s official forecast of a weak solar cycle. It could be just enough to catapult Terminators into the forefront of solar cycle prediction techniques.

Stay tuned. We’ll be back.

Feb. 17, 2022: New images from the Solar and Heliospheric Observatory (SOHO) are giving us a better look at yesterday’s farside explosion. SOHO coronagraphs recorded the most dramatic CME in years:

No, there won’t be a geomagnetic storm. The explosion happened on the farside of the sun, so the CME is heading away from Earth. We dodged a bullet.

Some readers have asked “How strong was the underlying solar flare?” We don’t know. Solar flares are classified by their X-ray output, but there are no spacecraft on the farside of the sun with X-ray sensors. Best guess: It was an X-flare.

You might suppose that the farside of the sun is hidden from view. However, researchers using a technique called “helioseismology” can make crude maps of the sun’s hidden hemisphere. Their latest map reveals a huge farside active region:

The black blob is a sunspot group–a big one–and it is the likely source of the explosion. According to Junwei Zhao of Stanford University’s helioseismology group, active regions this large are rare. “This is only the second farside active region of this size since September 2017,” he says.

Lucas Guliano, a solar scientist at the Harvard-Smithsonian Center for Astrophysics, believes the active region might be an old friend: AR2936, a sunspot that was on the Earthside of the sun in early February.

“If so, it is the same sunspot responsible for the geomagnetic storm that downed the SpaceX satellites on Feb. 4th,” he says.

Apparently it has grown since then. Based on its current location, the sunspot could emerge into view over the sun’s northeastern limb about 4 days from now. It could be quite a sight, so stay tuned. Solar flare alerts: SMS Text.