The Sun is about to experience an important event: a reversal of the magnetic field.
This phenomenon occurs approximately every 11 years and marks an important milestone in solar cycle. Polarity change shows half way solar maximumthe peak of solar activity and the beginning of the transition towards solar minimum.
The last time the sunThe reversal of the magnetic field occurred towards the end of 2013. But what causes this polarity change and is it dangerous? Let’s take an in-depth look at solar magnetic field reversal and study the effects it could have on Earth.
Related: How a giant sunspot sparked solar storms that spawned global auroras that dazzled us all
To understand magnetic field reversal, it is first important to become familiar with the solar cycle. This approximately 11-year cycle of solar activity is governed by the sun’s magnetic field and is indicated by the frequency and intensity of sunspots visible on the surface. The height of solar activity during a given solar cycle is known as the solar maximum, and current estimates predict it will occur between end of 2024 and beginning of 2026.
But there is another very important, although lesser known, cycle that encompasses 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 Space.com contributing editor, told Space.com.
During solar minimum, the sun’s magnetic field is close to a dipole, with a north pole and a 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 of the north and south poles,” French said. By the time solar maximum passes and solar minimum arrives, the sun has returned to a dipole, albeit with reversed polarity.
The next polarity change will be from the northern magnetic field to the southern magnetic field in the northern hemisphere and vice versa in the southern hemisphere. “This will bring it to a magnetic orientation similar to that of Earth, which also has its magnetic field oriented south in the northern hemisphere,” French explained.
What causes the polarity change?
The reversal is caused 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 ejections (CME) – large explosions of plasma and magnetic field.
As sunspots emerge near the equator, they will have an orientation matching the old magnetic field, while sunspots forming closer to the poles will have a magnetic field matching the incoming magnetic orientation, said French. This is called Hale’s Law.
“The magnetic field from the active regions moves towards the poles and eventually causes the reversal,” says solar physicist Todd Hoeksema, director of the Wilcox Solar Observatory at Stanford University. previously told Space.com.
But the exact underlying cause of such polarity reversal remains mysterious. “It’s about the whole (solar) cycle and it makes you wonder what it is,” Phil Scherrer, a solar physicist at Stanford University, told Space.com. “We still don’t have a really coherent 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 where the magnetic field is coming from. “Will there be a lot of sunspots? And will the sunspots contribute to the pole’s magnetic field, or will they cancel out locally?” Hoeksema said. “This question we don’t yet know how to answer.”
How quickly is change happening?
What we do know is that the reversal of the solar magnetic field is not instantaneous. This is a gradual transition from a dipole to a complex magnetic field and then to an inverted dipole over the entire 11-year solar cycle. “In short, there is no specific ‘moment’ in which the sun’s poles reverse,” French said. “It’s not like on Earth, where the reversal is measured by the migration of the North/South pole.”
It usually takes a year or two for complete reversal, but this can vary greatly. For example, the north polar field of solar cycle 24, which ended in December 2019, took almost five years to reverse, according to the National Solar Observatory.
The reversal of the magnetic field is so gradual that you won’t even notice it. And no, as dramatic as it sounds, it’s not a sign of an impending apocalypse. “The end of the world will not end tomorrow”, Scherrer said previously Espace.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, triggering many powerful solar flares and CMEs, triggering strong geomagnetic storms on Earth, which, in turn, produced a few geomagnetic storms. incredible auroras lately.
However, the increased severity of space weather is not the direct cause of the polarity reversal. Rather, these things tend to happen together, Hoeksema told Space.com in 2013.
According to French, space weather is typically strongest during solar maximum, when the solar magnetic field is also most complex.
One of the side effects of changing the magnetic field is slight but primarily beneficial: it can help protect Earth from galactic attacks. 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 moves, the “current sheet” – a sprawling surface that radiates billions of miles from the sun’s equator – becomes very wavyproviding a better barrier against cosmic rays.
Predicting future forces of the solar cycle
Scientists will closely monitor the reversal of the Sun’s magnetic field and see how long it takes to return to a dipolar configuration. If this happens in the next two years, the next 11-year cycle will be relatively active, but if the accumulation is slow, the cycle will be relatively weak, like the previous 24 solar cycle.