The Sun Is About To Lose Its Memory

That's the surprising conclusion of a new study by researchers at the University of Oulu in Finland. The team examined 180 years of the aa index (a record of geomagnetic activity stretching back to 1844) and found that after odd-numbered solar cycles, the sun forgets what happened in the past.

We're approaching such a moment now, as Solar Cycle 25 descends from its peak.

Their research begins with the little-known "Gnevyshev-Ohl rule." Discovered in 1948, this rule says that solar cycles come in pairs, with the odd-numbered half stronger than the even. Take a look at this historical plot of sunspot numbers:

Once you notice the Gnevyshev-Ohl rule, you can't unsee it. With only one exception in the past 180 years (Solar Cycles 22-23), odd cycles are always stronger than evens. The current pair, Cycles 24-25, definitely follow the rule.

The study found that when an odd cycle ends, the memory is erased. Nothing in the aa record predicts how strong the next cycle will be. The sun simply starts over.

Solar Cycle 26 begins in ~2030. If this research is correct, forecasters won't get a meaningful read on the new cycle until it is already underway, when new sunspots start writing their own detailed forecast.

Note: The Centennial Gleissberg Cycle may have something to say. This is a 90 to 100-year swell that modulates the height of solar cycles. We reported on the phenomenon in 2025. The Gleissberg tide is currently rising, suggesting that the next pair of solar cycles will be stronger than the last.

What will Solar Cycle 26 bring? No one knows--maybe not even the sun.

Source: https://spaceweather.com/