Solar Cycle 25 began last year. Forecasters thought it would be mild, but it turns out to be quite the opposite. Since its inception, this solar cycle has consistently exceeded predictions, producing more sunspots and spewing far more solar wind, flares and eruptions than the world’s leading experts predicted.
But while most space weather scientists scratch their heads saying “We still know very little about our star”, a heliophysicist has become the dark horse of space weather forecasting. His model of SunThe behavior of seems to have got it right.
A brief glance at the sun’s radiant disc reveals little about the starhis vibrant life. As ordinary Earthlings, we feel more affected by the pesky clouds obstructing its rays. But astronomers with telescopes have known since the 17th century that the sun’s surface changes from day to day, coming off as dark spots that grow and shrink, change shape and move across the sun’s surface, and disappear over time to be replaced by new ones. . Since 1749, astronomers have carefully recorded these sunspots. Around the middle of the 19th century, they realized that the number and size of these spots fluctuated according to an evolution roughly 11 year solar cycle. Since recordings began, the star has completed 24 cycles, with cycle 25 currently underway.
But there is more to this ebb and flow. Just as the number of sunspots waxes and wanes during the same cycle, the productivity of these cycles varies from one cycle to another, according to as yet little explored patterns.
Related: Wild solar weather knocks satellites out of orbit. It will only get worse.
The two predictions
Cycle 24, which officially ended in December 2019 but overlapped cycle 25 that followed for quite a while, was one of the weakest on record. When a group of experts from NASA and the National Oceanic and Atmospheric Administration (NOAA) came together to estimate the sun’s activity for cycle 25, they predicted that the coming cycle would be just as weak.
But around the same time, another forecast came out. Made by a team led by Scott McIntosh, a solar physicist and deputy director of the US National Center for Atmospheric Research, this forecast predicted the exact opposite: this Cycle 25 could be among the strongest in recorded history.
“We looked at over 140 years of data on the sun’s magnetic activity and its relationship to sunspot number,” McIntosh told Space.com. “And there was a pattern that shaped the size or size of the sunspot cycle to come. We predicted that the same pattern would occur before solar cycle 25. Based on that, we made a wild scientific guess that cycle 25 could possibly be up to twice the amplitude of cycle 24.”
The team published their predictions in the newspaper Solar Physics (opens in a new tab) in November 2020. Since then, while NOAA and NASA experts were puzzled, McIntosh and his colleagues watched the sun do exactly what they expected.
For example, while NOAA and NASA predicted a measly 27 sunspots for December 2021, the sun produced 67, more than double the estimate. And in May 2022, instead of the 37 sunspots predicted by NOAA and NASA, there were 97, producing solar flares and coronal mass ejections. Intense solar activity has also caused geomagnetic storms on Earth, wreaking havoc on orbiting satellites and triggering magnificent aurora borealis.
The official forecast for the peak of the solar maximum, which is expected in April 2025, is 115 sunspots that month. But if the curve follows the current trend, which reflects the predictions of McIntosh and his team (opens in a new tab)the sun will easily reach 115 monthly sunspots by the end of this year and peak two years later at over 210 monthly sunspots.
“It’s really crazy that the sun keeps doing this,” McIntosh said. “Month after month it continues to follow the trail. But we’ll see. The sun does weird things sometimes, and the cycle could completely collapse tomorrow.”
Tzu-Wei Fang, a space scientist at NOAA’s Space Weather Prediction Center, agrees that official predictions of the solar cycle don’t work and admits that scientists’ current understanding of the factors that determine the sun’s behavior is rather limited.
“We don’t know what is driving this strong solar activity,” Fang told Space.com. “The behavior of the sun changes according to different cycles, from short cycles of 11 days to long cycles of 80 years. There are still a lot of unknowns, and we just don’t have enough data points or knowledge. for [accurately predict] solar activity.
The Hale Cycle
So what, exactly, are McIntosh and his colleague basing their “wild scientific guess” on? The team investigated the relationship between the roughly 11-year cycle of sunspot generation and the so-called Hale cycle, a 22-year cycle of magnetic activity in which magnetic waves of opposite polarity travel from poles of the sun towards the equator, where they eventually meet and cancel each other out.
The Hale cycle, discovered in the early 20th century by American astronomer George Ellery Hale, is likely driven by the so-called solar dynamo, the movement of molten matter in the sun’s core that generates the sun’s magnetic field . The Hale cycle includes two sunspot cycles, with the star’s magnetic poles swapping at the end of each sunspot cycle. The Hale cycle ends after 22 years, when the magnetic field returns to its original state.
McIntosh and his colleagues believe that the interference of magnetic waves during the Hale cycle leads to the creation of spots on the surface of the sun.
“For the past decade, we have been tracking the evolution of the Hale cycle,” McIntosh said. “Once you know what you’re looking for, you can go all the way back to 1860 and extract those features from sightings at the dawn of photography.”
Scientists modeled the progression of the magnetic cycle and compared it to historical observations of sunspots. They found a corresponding pattern: at the start of each new 11-year cycle, sunspots appear at mid-solar latitudes and only later begin to appear closer and closer to the equator, matching the movement of these sunspots. magnetic waves.
“It takes [the magnetic waves] about 19 years to reach the equator but when they meet and then literally over the course of a few months the sun goes from having [sunspot] activity at the equator to have nothing,” McIntosh said. “And when it comes to having nothing, then new activity springs to life at mid-latitudes and a new sunspot cycle begins.”
This “meeting in the middle” occurs when the opposing magnetic fields neutralize each other. The event appears to end the previous solar cycle and kick off the new one, leading scientists to dub the event “the terminator”. Exactly how this termination event occurs appears to have particular significance for the strength of the next solar cycle, McIntosh said.
“We first spotted [the terminator] about nine years ago,” McIntosh said. “And when we looked at the 140 years of data, we were able to make raw measurements of these termination events at the equator and measure the overlap of the magnetic systems. When you plot that against the strength of the upcoming cycle, you get a very strong linear relationship.”
The data seemed to suggest that the longer the time between terminators, the weaker the next solar cycle.
The terminator between solar cycles 24 and 25 was delayed a bit, McIntosh said; solar cycle 24 didn’t seem to want to go away. The event finally happened in December 2021, allowing McIntosh’s team to finalize their solar cycle prediction.
“It will be just above the historical average with a smoothed monthly sunspot count of 190 ± 20,” McIntosh said. Space Weather Archives (opens in a new tab) in February.
Fang, however, warns that it’s too early to draw conclusions about the current solar cycle.
“The fact that we now have strong solar activity does not mean that we are definitely looking at a much higher solar cycle,” she said. “It still needs work for scientists before we can draw that conclusion.”