(ORDO NEWS) — So far, almost every day in 2022, it has flared up in the form of flares and coronal mass ejections, some of which have been the most powerful eruptions our star is capable of.
In itself, the erupting Sun is not something strange. It erupts regularly, going through periods of high and low activity lasting approximately 11 years.
Current activity is well above official NASA and NOAA forecasts for the current solar cycle, and solar activity is consistently above forecasts as early as September 2020. But a scientist who studies solar activity will tell you that even this is not so strange.
“We can’t reliably predict solar cycles,” solar astrophysicist Michael Wheatland of the University of Sydney, Australia, told ScienceAlert.
“We don’t fully understand the solar dynamo, which generates magnetic fields visible on the surface as sunspots, and which produces flares. This is one of the unsolved problems in astrophysics; the imprecision in prediction is not surprising.”
No wonder, of course. But what if this lack of surprise – that we expect poor prediction of solar cycles – means we need to completely rethink how we do it? What if we are basing our predictions on the wrong metric?
11 to 22 years old
Solar cycles have a huge impact on the solar system, but are relatively poorly understood. Scientists have found that they are inextricably linked with the solar magnetic field, which in the form of arcs, vortices and loops crosses the surface of the Sun.
Approximately every 11 years, the magnetic poles of the Sun change places: the north becomes the south and vice versa. This switch coincides with the so-called solar maximum, characterized by a peak in sunspot activity, flares, and coronal mass ejections (CMEs).
After such a reversal, activity decreases and then rises again to a peak. It is in this phase that we are now – in the escalation phase of the current cycle, the 25th in a row since the beginning of the count.
Activity cycles are characterized and predicted based on one indicator: the number of sunspots observed on the Sun.
These are temporary regions where magnetic fields are particularly strong, which contribute to flare and CME eruptions. They appear as dark spots because the magnetic field impedes the flow of hot plasma, and these regions subsequently become colder and dimmer than their surroundings.
According to solar physicist Scott McIntosh of the US National Center for Atmospheric Research, predicting solar cycles based on sunspot numbers is a challenge.
“The sunspot cycle is not the main thing. It’s a secondary thing,” he told ScienceAlert. “And the way the canon is written, the way textbooks are written, the way solar activity is presented, is portrayed as primordial.”
“The problem is that this is not really the case, and the main one is the Hale cycle, the 22-year magnetic cycle. And the sunspot cycle is just a tiny subset of that big picture.”
The Hale cycle was discovered in the early 20th century by the American astronomer George Ellery Hale. It consists of two 11-year sunspot cycles – the time it takes for the poles to switch places twice, thereby returning to their original position.
Hale cycles, unlike 11-year cycles, are observed in a number of phenomena. This is a change in the magnetic polarities of both sunspots and solar magnetic poles, as well as the intensity of galactic cosmic rays on Earth.
Solar activity makes it difficult for cosmic rays to reach Earth, but odd and even solar cycles have different cosmic ray waveforms. This is due to the polarity of the solar magnetic field.
Explanation of sunspots
It is important to understand that we do not have a clear idea of what is happening inside the Sun. It is believed that the solar magnetic field is generated by a dynamo inside the star – a rotating, convective and electrically conductive fluid that converts kinetic energy into magnetic energy, spinning the magnetic field in space around the Sun.
If so, what causes sunspots? According to existing models, they are associated with the rotation of the Sun. The solar equator rotates faster than the poles.
If the straight lines of a magnetic field running longitudinally were pulled along with this rotation, they would stretch and eventually entangle, creating temporary, localized regions of a strong magnetic field, or sunspots.
This, McIntosh says, is based on the fact that the magnetic field is passive.
“You have a very complex system inside the sun. As with all physical systems, we make simplifications or approximations to try to understand what’s going on,” he explained.
“About 60 years ago, they made an approximation for magnetic fields – that they are small compared to the liquids in the Sun. So when the Sun circulates, like our planet, rotation leads to circulation, heating of the atmosphere leads to circulation, and with all this circulation, magnetic fields are simply dragged along with the circulation.”
Animations demonstrating this effect agree very well with sunspot observations: the initial magnetic fields appear at about a latitude of 30 degrees. But according to McIntosh and his colleagues, that’s because the model was designed to explain just that, and that alone.
There is an alternative explanation: Sunspots are an interference pattern generated by the magnetic fields of overlapping Hale cycles.
McIntosh and his colleagues first noticed a pattern that appeared in sunspot data in 2011, an overlay of so-called butterfly diagrams. These are graphs that show the occurrence of sunspots by latitude over time.
Noticing this, the researchers found and studied all the historical data on sunspots that they could get their hands on, up to the 1860s.
They found that such overlap continues to appear. Towards the end of one sunspot cycle, as the sunspots appear closer and closer to the equator, at mid-latitudes one can observe the appearance of sunspots of the next cycle.
According to the researchers, this indicates that oppositely polarized bands of magnetic activity pass their way through the Sun in cycles; they are responsible for, but not controlled by, the sunspot cycle. Moreover, cycles can interact; when two cycles of opposite polarity overlap, they interfere with each other.
As a result, magnetic systems mutually suppress the formation of sunspots, and a period of minimum solar activity sets in.
“The sunspot cycle is the result of an interaction between these large magnetic cycles,” McIntosh said in an interview with ScienceAlert. “In other words, it’s like an interference pattern. Magnetic fields tend to cancel each other out all the time.”
More data, always more data
Based on the “interference pattern” results, McIntosh and his team came up with current solar cycle predictions that are more in line with current observations than official predictions based on sunspot numbers.
However, at this stage, all this is theoretical.
We still don’t know, for example, what drives the magnetic activity bands on the Sun; researchers think it could be gravitational waves, but at the moment we don’t have enough information to say so.
“Scott McIntosh’s ideas are interesting, and the McIntosh/Lemon [this is Robert Lemon of the University of Maryland’s Goddard Institute for Planetary Heliophysics] prediction for cycle 25 is closer than the official one at this stage.
However, it’s not based on a physical model. I doubt it has greater predictive power than other observational forecasting approaches,” Whitland told ScienceAlert.
To find out more, we’ll need more data, which will take time.” According to McIntosh, this means looking at the Sun at high latitudes, near the poles, when a new cycle is forming.
We don’t normally see the solar poles as the Earth revolves around the solar equator, but the European Space Agency’s Solar Orbiter will fly over them just as the new cycle begins.
McIntosh thinks there is something about his team’s prediction being closer to how cycle 25 happened. At the very least, the ideas of the team deserve closer attention and serious study.
“We’ve been practically wrong for about 10 years, but it hasn’t caught on in the scientific community,” he said.
“This solar cycle presented an opportunity. Since our prediction was so diametrically opposed to what the consensus group was showing, it means that if we get close, then we really need to take another look at how stars create magnetic fields.”
“Maybe it’s closer to what we’re seeing than the old way. And it could be a hybrid, a mixture of the two. Maybe it is.”
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