The Next Solar Cycle Has Started… But the Current One Hasn’t Finished Yet

We may be already seeing the makings of next solar cycle, peeking out through the current one.

It’s been a wild ride. Thus far, Solar Cycle Number 25 has been one of the strongest cycles in recent memory, producing several massive sunspot groups. The current large region turned Earthward (Active Region 3780) is now easily visible with eclipse glasses… no magnification needed. Cycle 25 started back in 2019.

A Stormy Year

To be sure, the latest solar cycle will be one for the history books, as it heads towards an active maximum in 2025. But even though Cycle 25 will run out through the remainder of the current decade, there are already signs that Cycle 26 could be beginning, just under the roiling solar surface. A study out of the University of Birmingham recently presented at the Royal Astronomical Society’s National Astronomical Meeting in Hull (United Kingdom) shows that key indicators for the start of the next cycle may already be in place.

Numbering the solar cycle under current the convention goes all the way back to the start of Cycle 1 in 1755. The pattern for numbering cycles was started in 1852 by astronomer Rudolf Wolf.

We know that a new solar cycle has formally started when sunspots appear at higher solar latitudes. These also typically have a reversed polarity, versus the previous cycle. These then push down near the solar equator as the cycle progresses. Spot from two cycles can also mix as the transition gets underway.

Laying out spots from successive cycles versus latitude creates a butterfly diagram that demonstrates this effect, in what’s known as Spörer’s Law.

Peering Inside the Sun

But there’s more to the Sun than meets the eye. As a large ball of hydrogen and helium gas, the Sun does not rotate as a single solid mass. Instead, it rotates faster at the equator (25 days) versus near the poles (34 days). Scientists can probe the solar interior via a method known as solar helioseismology, which looks at waves crossing the solar photosphere in an effort to model the interior.

These internal sound waves form bands in a phenomenon known as solar torsional oscillation. Faster-rotation belts appear as a harbinger of the next cycle. These move along with visible sunspots towards the solar equator as the cycle progresses.

“The indication of Cycle 26 that we see is that the solar rotation has been speeding up at around 50 degrees latitude and now appears to be leveling off,” Rachel Howe (University of Birmingham) told Universe Today. “This forms part of a pattern called the torsional oscillation, where bands of slightly faster and slower rotation emerge at mid-latitudes before the cycle officially starts and move down to lower latitudes, alongside the sunspot activity, as the cycle develops. In earlier cycles we have seen that the faster-rotating band associated with the cycle can be traced back to around the maximum of the previous cycle, and we think we’re seeing the beginning of the pattern again. It will still be several years before we can expect to see sunspots belonging to the new cycle, though!”

Monitoring the Sun Around the Clock

The Global Oscillation Network Group (GONG) makes the science of helioseismology possible. This is a worldwide network that monitors the Sun continuously. In space, the Helioseismic Magnetic Imager aboard the joint ESA/NASA Solar and Heliospheric Observatory (SOHO) compliments this effort. The Michelson Doppler Imager (MDI) on NASA’s Solar Dynamics Observatory (SDO) also plays a key role in this campaign. This effort goes back to 1995, spanning the last three solar cycles.

This gives researchers a look at the start of the last two solar cycles. It also hints at what might be in store for the start of Solar Cycle 26. “If we can understand how this flow pattern relates to the sunspot cycle, we may be able to do better at predicting how strong the next solar maximum will be and when it will occur,” says Howe.

Solar Cycle 25 has thus far been extremely active, far beyond expectations. This follows the historic lull that preceded it between Cycles 24 and 25. Observers saw few sunspots during this profound minimum. Still, this fell in line with many predictions made by astronomers who study the Sun, suggesting a stronger than usual cycle on rebound.

Looking Ahead to Cycle 26

“The Sun is always surprising,” says Howe. “Some of the most exciting discoveries recently have come from the spacecraft—Solar Orbiter and Parker Solar Probe—that are flying closer to the Sun than ever before, helping scientists to unravel the connections between what we see on the Sun’s surface and the ‘space weather’ events that affect us on Earth. We’re looking at the surface of the Sun in more detail than ever before, but there’s also a place for long-term studies (which this work is a part of) that follow the large-scale patterns inside the Sun over decades.”

The May 10^th solar storm was thus far the most impressive one of the cycle. This storm sent aurora to latitudes far south as Spain and Mexico, areas where aurorae are rarely seen. We were treated to a persistent red glow watching from central Germany, an unforgettable sight.

Solar Cycles and More

Historically, the Wolf Sunspot Number defines the level of solar activity. Astronomers refer to this as the Relative or Zürich Sunspot Number. One 2013 study suggested that the orientation and strength of the heliospheric current sheet is a better indicator of the health of the current solar cycle, rather than the sunspot number.

We usually say it’s an 11-year solar cycle from one minima/maxima to the next… but it’s actually double that length. The Sun’s magnetic field flips every 11-years, returning to the same relative orientation every 22 years.

We see ‘starspot cycles’ on other suns as well. It is also unclear why an 11-year cycle is ‘baked in’ to our Sun. We’re also unsure if this has always been the case throughout its 4.6-billion year life span.

This research provides a great model to test the next solar cycle, as we struggle to understand and live with our tempestuous star.

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