The Sun is on the cusp of an important event: a magnetic field reversal.
This phenomenon occurs approximately every 11 years and marks an important milestone in solar cycle. The change in polarity indicates the halfway point of the solar maximumthe height of solar activity and the beginning of the shift to solar minimum.
The last time the sunThe magnetic field reversal was towards the end of 2013. But what causes this polarity change and is it dangerous? Let’s take a closer look at the reversal of the sun’s magnetic field and explore the effects it may have on the The Earth.
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To understand the reversal of the magnetic field, it is first important to be familiar with the solar cycle. This approximately 11-year cycle of solar activity is driven by the solar magnetic field and is indicated by the frequency and intensity of sun spots visible on the surface. The height of solar activity during a given solar cycle is known as the solar maximum, and current estimates predict that it will occur between end of 2024 and beginning of 2026.
But there is another very important, if lesser-known, cycle that encapsulates two 11-year solar cycles. Known as the Hale cycle, this magnetic cycle lasts approximately 22 years, during which the sun’s magnetic field reverses and then returns to its original state. Ryan Frenchsolar astrophysicist and writer for Space.com, told Space.com.
During solar minimum, the sun’s magnetic field is near a dipole, with one north pole and one south pole, similar to Earth’s magnetic field. But as we move toward solar maximum, “the sun’s magnetic field becomes more complex, with no clear separation between north and south poles,” French said. By the time solar maximum passes and solar minimum occurs, the sun has returned to a dipole, albeit with reversed polarity.
The upcoming polarity reversal will be from the north to south magnetic field in the Northern Hemisphere and vice versa in the Southern Hemisphere. “This would bring it to a similar magnetic orientation as Earth, which also has a southward magnetic field in the Northern Hemisphere,” French explained.
What causes the polarity to change?
The rotation is driven by sunspots, magnetically complex regions on the sun’s surface that can give rise to significant solar events such as solar flares and coronal mass ejection (CMEs) — large bursts of plasma and magnetic field.
As sunspots form near the equator, they will have an orientation consistent with the old magnetic field, while sunspots forming closer to the poles will have a magnetic field consistent with the incoming magnetic orientation, French said. This is called Hale’s Law.
“The magnetic field from the active regions makes its way to the poles and eventually causes the reversal,” solar physicist Todd Hoeksema, director of the Wilcox Solar Observatory at Stanford University, Space.com previously said.
But the exact underlying reason for such a polarity reversal remains mysterious. “It goes into the whole [solar] cycle and I’m wondering what it is,” Stanford University solar physicist Phil Scherer previously told Space.com. “We still don’t have a really self-consistent mathematical description of what’s going on. And until you can model it, you don’t really understand it — it’s hard to really understand it.”
It really depends on where the magnetic field is coming from. “Will there be a lot of sunspots? And will sunspots contribute to the pole’s magnetic field, or will they cancel out locally?” Hoeksema said. “That question we still don’t know how to answer.”
How fast is the switching done?
What we do know is that the reversal of the sun’s magnetic field is not instantaneous. This is a gradual transition from a dipole to a complex magnetic field, to an inverted dipole throughout the 11-year solar cycle. “In short, there is no specific ‘moment’ at which the solar poles reverse,” French said. “It’s not like on Earth where the reversal is measured by the north/south pole migration.”
It usually takes a year or two for a full turnaround, but it can vary widely. For example, the north polar field of solar cycle 24, which ended in December 2019, took almost five years to reverse, according to National Solar Observatory.
The magnetic field reversal is so gradual that you won’t even notice when it happens. And no, as dramatic as it sounds, this is not a sign of an impending apocalypse. “The World Won’t End Tomorrow,” Scherer said earlier Space.com.
However, we will experience some of the side effects of polarity reversal.
How does the sun’s magnetic reversal affect us?
There is no doubt that the sun has been incredibly active recently, firing off numerous powerful solar flares and CMEs, triggering strong geomagnetic storms on Earth, which in turn have produced some amazing auroral displays lately.
However, the increased burden of space time is not the direct cause of the polarity reversal. Rather, these things tend to happen together, Hoeksema told Space.com in 2013.
Space weather is typically strongest during solar maximum, when the sun’s magnetic field is also most complex, according to French.
One side effect of the magnetic field shift is mild but mostly beneficial: it can help protect Earth from galactic cosmic rays — high-energy subatomic particles that travel at near the speed of light and can damage spacecraft and harm orbiting astronauts who are outside Earth’s protective atmosphere.
As the sun’s magnetic field shifts, the “fluid”—a stretched surface that radiates billions of miles outward from the sun’s equator— it gets very wavyproviding a better barrier against cosmic rays.
Predicting the strength of the future solar cycle
Scientists will keep a close eye on the sun’s magnetic field reversal and see how long it takes for it to bounce back to a dipole configuration. If this happens in the next few years, the next 11-year cycle will be relatively active, but if the accretion is slow, the cycle will be relatively weak, like the previous Solar Cycle 24.
