The reversal could have a beneficial effect on Earth.
The sun is on the verge of a significant event: a magnetic
field reversal.
This phenomenon happens roughly every 11 years and marks an
important stage in the solar cycle. The shift in polarity indicates the halfway
point of solar maximum, the height of solar activity, and the beginning of the
shift toward solar minimum.
The last time the sun's magnetic field flipped was toward
the end of 2013. But what causes this switch in polarity, and is it dangerous?
Let's take a deep look at the sun's magnetic field reversal and investigate the
effects it could have on Earth.
To understand the magnetic field's reversal, first, it's
important to be familiar with the solar cycle. This approximately 11-year cycle
of solar activity is driven 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 solar maximum, and current
estimates predict it will occur between late 2024 and early 2026.
But there is another very important, albeit lesser-known,
cycle that encapsulates two 11-year solar cycles. Known as the Hale cycle, this
magnetic cycle lasts approximately 22 years, through which the sun's magnetic
field reverses and then reverts to its original state, Ryan French, a solar
astrophysicist and Space.com contributing writer, told Space.com.
During solar minimum, the sun's magnetic field is close to a
dipole, with one north pole and one south pole, similar to Earth's magnetic
field. But as we shift toward solar maximum, "the sun's magnetic field
becomes more complex, without a clear north-south pole separation," French
said. By the time solar maximum passes and solar minimum arrives, the sun has
returned to a dipole, albeit with a flipped polarity.
The upcoming switch in polarity will be from the northern to
southern magnetic field in the Northern Hemisphere and vice versa in the
Southern Hemisphere. "This will bring it to a similar magnetic orientation
to Earth, which also has its southern-pointing magnetic field in the Northern
Hemisphere," French explained.
What causes the switch in polarity?
The reversal is driven by sunspots, magnetically complex
regions of the sun's surface that can spawn significant solar events, such as
solar flares and coronal mass ejections (CMEs) — large blasts of plasma and
magnetic field.
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During solar maximum a large number of sunspots are visible
at mid-latitudes and during solar minimum a very small number (sometimes zero)
of sunspots are visible at the equator.
(Image credit: Future) |
As sunspots emerge close to 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, French said. This is called Hale's law.
"The magnetic field from active regions makes its way toward the poles and eventually causes the reversal," solar physicist Todd Hoeksema, director of the Wilcox Solar Observatory at Stanford University.
But the exact underlying cause of such a flip in polarity
remains mysterious. "That gets into the whole [solar] cycle, and wondering
what that is," Stanford University solar physicist Phil Scherrer
previously told Space.com. "We still don't have a really self-consistent
mathematical description of what's happening. 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 comes from.
"Are there going to be many sunspots? And are the sunspots going to
contribute to the magnetic field of the pole, or are they going to kind of
cancel locally?" Hoeksema said. "That question we don't yet know how
to answer."
How quickly does the switch occur?
What we do know is that the solar magnetic field flip is not
instantaneous. It's a gradual transition from a dipole to a complex magnetic
field, to a reversed dipole over the entire 11-year solar cycle. "In
short, there is no specific 'moment' in which the sun's poles flip,"
French said. "It's not like the Earth, where the flip is measured by the
migration of the North/South pole."
It generally takes a year or two for a complete reversal,
but it can vary significantly. For example, the north polar field of Solar
Cycle 24, which ended in December 2019, took nearly five years to reverse,
according to the National Solar Observatory.
The magnetic field flip is so gradual, you won't even notice when it happens. And no, however dramatic it might sound, it is not the sign of an impending apocalypse. "The world will not end tomorrow," Scherrer previously told.
However, we will experience some of the polarity flip's side
effects.
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