The Sun has recently experienced an uptick in activity, with lots of sunspots accompanied by flares, coronal mass ejections, and visible auroras — but experts still expect a mild solar cycle.
The Sun has been very active lately. Since the solar cycle picked up steam last year the number of sunspots and solar flares has constantly increased until it suddenly ramped up between December 2022 and January 2023. On April 21st, a coronal mass ejection propelled a pulse of plasma — super-heated magnetized gas — toward Earth, causing a geomagnetic storm that ranked at level 4 in the 5-degree scale used by the U.S National Oceanic and Atmospheric Administration (NOAA). The storm treated skygazers to bright auroras that extended as far south as New Mexico in the U.S, or France and Germany in Europe.
This peak in solar activity has prompted many to wonder if the current solar cycle is becoming more active than scientists had predicted.
The Sun goes through cycles of magnetic activity that last 11 years on average, during which its magnetic poles swap places. The active phase toward the middle of the cycle is marked by frequent sunspots, flares, and eruptions , followed by a quiet period where sunspots may disappear for days or weeks at a time and flares are uncommon. The solar cycles also vary in intensity from one to the next. The last cycle, which numbered 24 since systematic sunspot monitoring began, was one of the quietest on record.
In their attempt to understand this variability and what causes it, scientists predict the exact duration and intensity of each solar cycle based on a variety of methods — from purely statistical models using observations of previous cycles to complex simulations of solar physics. An international group of experts, the Solar Cycle Prediction Panel, evaluates the merits of individual predictions and tries to come up with a unified forecast for the upcoming cycle.
Lisa Upton (Southwest Research Institute), cochair of the Solar Cycle 25 Prediction panel, says the activity we are seeing is normal for a cycle reaching its maximum and still matches the panel’s prediction of a weak cycle, on par with or slightly more active than solar Cycle 24. “As humans our memories tend to be short, and it has been a decade since we’ve been in solar cycle maximum,” Upton says, “so people have forgotten what activity on the Sun looks like.”
Other scientists, however, think that the panel’s predictions fall short, and that we are witnessing a cycle that could end up being more powerful than expected.
In 2020 Scott McIntosh (National Center for Atmospheric Research) and collaborators predicted in Solar Physics that Cycle 25 was going to not only be stronger than the previous cycle but it could be one of the most powerful ever recorded. Looking at historical records, they observed a link between the timing of the end of each solar magnetic cycle and the strength of the subsequent sunspot cycle.
The full solar magnetic cycle, during which the Sun’s magnetic field switches twice, returning the poles to their original position, is known as Hale Cycle and takes 22 years. McIntosh and colleagues hypothesize that this cycle is governed by vast magnetic bands of opposing sign that move across the surface of the Sun. When these meet at the solar equator, they cancel out in a terminator event, which occurs twice every Hale cycle.
McIntosh’s 2020 prediction, however, counted on the Terminator Event occurring in mid-2020, but it didn’t happen until December 2021. This led McIntosh and colleagues to issue a more moderate prediction that pointed to a shorter cycle that would be above average in terms of the magnitude of activity.
Same Data, Different Interpretations
At this point, it isn’t clear who’s right. The amount of sunspots and solar flux that briefly went haywire earlier this year, reaching a peak of 146 sunspots in January, have largely declined to levels within the panel’s prediction.
McIntosh thinks that the cycle is matching his own prediction. “It’s tracking very well,” he says, “This month has been a little low, but in general it’s following the projection very well.”
However, while Upton admits that the cycle currently looks a tad more active than the panel had expected, she says every cycle fluctuates. She says the current cycle doesn’t look anywhere near like an average cycle, such as Cycle 23, or like a strong one, such as Cycles 21 and 22 that saw more than 250 sunspots at a time.
“Do we have this completely nailed down? Obviously not,” Upton says. “But I think we are getting really good at narrowing the gap between what we can do with our predictions and what we are actually seeing.”
Still, it seems that we will have to wait to the solar maximum, expected late in 2024 or early in 2025 to see how this ends. “The Sun loves to throw us for loops,” Upton concludes.