The Sun is on the verge of a major event: the reversal of its magnetic field. This phenomenon occurs approximately every 11 years and marks an important stage in the solar cycle. The polarity shift 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 towards the end of 2013. But what causes this polarity switch and is it dangerous? Let’s take a deep look at the reversal of the sun’s magnetic field and explore the effects it could have on Earth.
To understand the reversal of the magnetic field, first, it is important to become familiar with the solar cycle. This roughly 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 that it will occur from late 2024 to early 2026.
But there is another very important, though less well known, cycle that includes two solar cycles of 11 years. Known as the Hale cycle, this magnetic cycle lasts about 22 years, during which the sun’s magnetic field reverses and then returns to its original state.
During solar minimum, the Sun’s magnetic field is near a dipole, with a north 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 north-south divide. By the time solar maximum passes and solar minimum is reached, the Sun has returned to a dipole, albeit with a polarity reversal.
The upcoming polarity change will be from the north to the south magnetic field in the northern hemisphere and vice versa in the southern hemisphere. This would bring it into a similar magnetic orientation to Earth, which also has a southerly magnetic field in the northern hemisphere.
The solar explosions
The reversal is caused by sunspots, magnetically complex regions of the Sun’s surface that can cause major solar events such as solar flares and coronal mass ejections (CMEs) that are large bursts of plasma and magnetic field. These explosions when caused at points of the Sun that at that moment see the Earth send to our planet a tsunami of charged particles which cause natural phenomena such as the aurora but at the same time cause operational problems in telecommunication satellites and electrical networks.
During solar maximum a large number of sunspots are visible in the mid-latitudes, and during solar minimum a very small number (sometimes zero) of sunspots are visible at the equator. As sunspots emerge near the equator, they will have an orientation that matches the old magnetic field, while sunspots that form closer to the poles will have a magnetic field that matches the incoming magnetic orientation. This is called Hale’s Law.
The magnetic field from active regions is directed towards the poles and eventually causes the reversal.
But the exact underlying cause of such polarity reversal remains mysterious. This goes into the whole solar cycle and I wonder what that is. We still don’t have a really consistent mathematical description of what’s going on. And until we can model it, it’s hard to really understand.
It really depends on where the magnetic field is coming from. Will there be many sunspots? And will sunspots contribute to the pole magnetic field or cancel out locally? To this question we do not yet know how to answer.
