Sun's "Battle Zone" and "Solar Maximus", What Are They?

Scientists have reported that we have officially entered solar maximum. But they also warned that the sun's activity won't actually peak until after this explosive phase is over and we enter the solar "battle zone."

This relatively understudied phase of the solar cycle, where giant coronal holes emerge on the sun, could be disastrous for Earth-orbiting satellites, which have exponentially multiplied since the last solar cycle, experts warn.

Solar maximum is defined as the period of the sun's roughly 11-year solar cycle, or sunspot cycle, when the number of visible dark patches on the sun is at its highest. During this time, powerful solar flares explode from the solar surface and hurl clouds of charged particles at Earth, triggering intense geomagnetic storms that paint vibrant auroras across the night sky.

Halfway through this period, the sun's magnetic field completely flips, leading to an eventual reduction in sunspots and solar activity until we reach "solar minimum" and the next solar cycle begins.

Solar activity has been ramping up over the last few years, hinting that solar maximum could arrive sooner and be more active than scientists initially expected. Last month, space weather experts confirmed this was the case when they announced that solar maximum is already well underway, and could last for around a year or more.

But on 15 November, Lynker Space, a new space weather prediction and solution company that formed earlier this year, released a blog post explaining that a newly realized phase of the solar cycle, known as the battle zone, will likely begin in the next year or two, as solar maximum ends.

Scott McIntosh, a solar physicist and Vice President of Lynker Space, told Live Science that geomagnetic activity in the upper atmosphere could increase by up to 50 percent during the battle zone, which could last well into 2028. "The potential for large, dangerous geomagnetic storms in the next few years is very real," he said.

In addition to the 11-year sunspot cycle that most people are familiar with, the sun also has a longer 22-year "Hale cycle," which is the time it takes for our home star's magnetic field to flip and then flip back again.

During this longer cycle, large bands of magnetism, known as Hale cycle bands, emerge at the sun's poles and slowly migrate toward the sun's equator, independent from the sun's wider magnetic field. A new band emerges in both of the sun's hemispheres during each solar maximum and lasts until the end of the next sunspot cycle, when the bands reach the sun's equator and disappear in what researchers call a "solar terminator" event. This means that during the first half of a sunspot cycle (from solar minimum to solar maximum) there is only one Hale cycle band in each of the sun's hemispheres. But during the second half of a cycle (after solar maximum), there are two bands in each hemisphere.

The overlap of these giant bands is what governs the sunspot cycle, McIntosh explained. When there is only one band in each hemisphere, there is a magnetic imbalance across the sun with weaker magnetic fields near the equator, allowing the number of black spots to increase around our home star's waist, he said.

But when a second band is established, it "reduces the imbalance" and makes it harder for sunspots to form, McIntosh added. "Eventually, over a few years, as the bands march towards the equator the imbalance progressively decreases until the sun can't make any sunspots."

Hale cycle bands have historically been overlooked by most space weather forecasters who rely more on sunspot numbers to predict solar activity. However, some scientists are starting to realize that the magnetic bands are more important than we thought. For example, studying the solar terminator event that preceded the current solar cycle allowed McIntosh and others to correctly predict the arrival of solar maximum when other experts did not.

The battle zone is a new term introduced by Lynker Space to describe the period when two Hale cycle bands are "vying for dominance" in each of the sun's hemispheres, McIntosh said.

"We are using this term to describe the fact that geomagnetic activity is enhanced after sunspot maximum," he added.