Stronger Solar Activity Cycles May Be in the Sun's Forecast

Yahoo

10-05-2025

A year ago this weekend, the sun's activity created some of the most spectacular auroras on record, with displays visible as far south as Florida.
The incredible spectacles last May (and another auroral outburst last October) were partly a matter of luck because several factors, some of them serendipitous, affect the appearance of aurora. But the sun had been primed to put on a show as it approached the maximum phase of its 11-year activity cycle—and that high activity continues today. This solar cycle still has the potential to cause more celestial spectacles before activity calms down. And scientists say that the coming solar cycles may be even more eventful. But it remains quite difficult to predict the sun's behavior.
'Solar storms—it's a probabilistic thing, so sometimes they don't always do what you would expect,' says Lisa Upton, a heliophysicist at the Southwest Research Institute.
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The sun is essentially a massive liquid magnet. Heliophysicists gauge our star's activity by tallying the number of sunspots—relatively 'cold' knots of its magnetic field that are often the source of radiation and plasma outbursts—on its surface. (Scientists monitor this tally in real time, but they evaluate the solar cycle's stages based on smoothed averages over many months. So the formal declaration of a cycle's solar maximum and minimum always happens after the fact.)
The number of sunspots naturally rises and falls over about 11 years, during which the sun's magnetic poles first strengthen, then weaken and finally flip. When the sun's magnetic field is calmest—with one pole that is firmly positive and one that is firmly negative—activity is at its minimum, as it was most recently around December 2019, and the star is sometimes entirely free of blemishes.
For more than a year now, the sun has been in the opposite phase—the solar maximum—with a messy magnetic field, plenty of sunspots and regular outbursts. August 2024 produced the most sunspots of any recent month, with more than 200 such storms.
Sunspots have since become less numerous, but it's still unclear whether the solar maximum is truly on its way out. 'We've had a little bit of a slowdown in activity [during] the last couple months. That's not too surprising,' Upton says. 'A question at this point, which will be interesting, is whether or not we're going to have another little spike in activity.'
She says that if such a spike were to happen, it would likely come within about three months, mirroring a small spike that occurred in June and July 2023. 'But the sun likes to surprise us,' Upton adds, 'so we'll see if that happens.'
Even as scientists watch the current solar cycle unfold, they're also working to understand what future cycles might bring.
That's a difficult task, given that modern science is only in the 25th activity cycle in which researchers have made plentiful sunspot observations. More sophisticated observations that help scientists understand the sun in detail, such as space-based observations and magnetic data, are even newer, with some offering insight into only a couple of solar cycles thus far. Scientists can study tree rings and ice cores to get a basic sense of solar activity before observations began, but these data are less detailed and don't provide precise sunspot counts.
One hypothesis suggests that the sun displays a longer-term variability called the Gleissberg cycle, named for astronomer Wolfgang Gleissberg, who posited such 80-year cycles in the 1960s. (Other proposed longer-duration cycles in solar behavior include the Suess–de Vries cycle, lasting 195 to 235 years, and the Hallstatt cycle, stretching over some 2,400 years.) And a new analysis of protons trapped in the inner radiation belt that surrounds Earth suggests a new Gleissberg cycle may be beginning.
Not all heliophysicists are sold on the Gleissberg cycle, however, given the scant data scientists have to work with. 'It's kind of debatable whether or not this is a physical phenomenon versus a statistical phenomenon,' Upton says.
Regardless, chances are good that during the coming solar cycles, the sun will be more active than it has been over the past two decades. That's because Solar Cycle 24, which dominated the 2010s, was one of the weakest on record—and the current cycle has remained below average in activity.
'We, as humans, have a short memory, and a lot of people have been wowed and amazed by what's been going on in the last year or two on the sun,' Upton says. 'There's this tendency for us to forget this longer-term variability in what the sun is doing.'
The sun's activity doesn't just paint our skies with spectacular auroras. The radiation and plasma outbursts the sun emits can have real consequences for terrestrial life: solar storms can interfere with satellites in orbit, including communication and navigation infrastructure, and serious incidents can even affect the power grid on Earth.
And if our technology is vulnerable to the set of phenomena collectively called space weather, human bodies are even more so. Fortunately, people on Earth's surface are well shielded from the sun's activity by a magnetic bubble that surrounds our planet and deflects much of the most dangerous emissions.
The risks of solar activity stretch throughout the solar system, however. As NASA and other space agencies look to send humans beyond orbit, to the moon and to Mars, these organizations will need to protect astronauts from the dangers of space weather—work that will include better predictions of what conditions these outer regions are likely to experience.
'As solar cycle activity ramps up—and it is very likely to do so because we are in weaker-than-average cycles—it's going to become more and more important to be able to understand space weather not just in the direction of Earth,' Upton says.