Sandra Chapman and her crew at the University of Warwick’s Centre for Fusion, Space and Astrophysics have recognized a sharp cutoff second inside each solar cycle — a level the place the solar’s most violent space weather stops almost overnight — and they say counting sunspots at that second can forecast the strength of the next cycle six to seven years before it peaks. Chapman is presenting the discovering this week at the Royal Astronomical Society’s National Astronomy Meeting in Birmingham.
The crew used the methodology to accurately name that Solar Cycle 25 would run stronger than mainstream forecasts steered. That name was vindicated when the May 2024 “Gannon” storm pushed the aurora as far south as Devon and Cornwall in the UK — and, worldwide, as far south as Mexico and Puerto Rico.
A sudden change, not a gradual fade
The solar’s roughly 11-year cycle has been mapped since the nineteenth century. Sunspot counts rise, peak, and fall as the star’s magnetic subject prepares to flip polarity. What Chapman’s group argues is that the descent isn’t gradual for the occasions that matter most to energy grids and satellites.
“The sun doesn’t gently go to sleep and then gently wake up again,” Chapman stated in the Warwick announcement. “Instead, we’ve discovered that the most extreme space weather switches off quite suddenly at a specific point in every solar cycle. By identifying that point, we’ve found a new way to predict how active the next solar cycle is likely to be.”
That switch-off level carries a signature. In a 2024 paper in Scientific Reports, Chapman and co-author Thierry Dudok de Wit confirmed that the clear cutoff of excessive space weather happens when greater than 90 p.c of solar active-region areas have migrated to inside about 15 levels of the solar equator, into the band the place solar differential rotation weakens. Read the fingerprint on the means down, and the form of the next climb turns into seen.
Why a six-year lead time issues
Existing solar cycle predictions sometimes agency up solely a 12 months or two before solar maximum, when precursor alerts in the solar’s polar magnetic fields grow to be measurable. That brief horizon leaves satellite tv for pc operators, grid managers, and airways with restricted time to harden infrastructure in opposition to a robust cycle.
The stakes will not be hypothetical. The March 1989 geomagnetic storm collapsed the Hydro-Québec grid in roughly 90 seconds, reducing energy to six million individuals in a Quebec winter. The 1859 Carrington storm did worse to a a lot smaller technological footprint. A comparable occasion at present would hit a much more electrified, satellite-dependent civilization.
A six-to-seven-year lead time modifications the calculus. Utilities plan grid upgrades on decadal timescales. Satellite constellations are procured years upfront. Knowing whether or not the next cycle will hammer the ionosphere or barely nudge it lets these choices be made with higher info.
The Cycle 26 preview
An early software of the approach — with the caveat that Cycle 25 has not but reached its switch-off — factors to a reasonable Solar Cycle 26 with a peak sunspot quantity of round 100 to 120. That would put the coming cycle at roughly the identical strength as Cycle 25, or barely weaker.
“We’re about two years away from the switch-off point for the current Solar Cycle 25,” Chapman stated. “At the moment, we have to estimate where that point will be, but once we reach it we can use observations alone to make a much more precise prediction for Solar Cycle 26. That will still give us around seven years’ warning of how strong the cycle is likely to be.”
Independent statistical work helps the reasonable outlook. Time-series analyses of month-to-month sunspot numbers additionally challenge Cycle 26 in a related reasonable vary, although by purely statistical approaches quite than by a bodily switch-off mechanism.
Validated by 2024’s auroral fireworks
The methodology’s credibility rests on Cycle 25. Official consensus forecasts predicted a weak cycle, related to the anemic Cycle 24. The switch-off method flagged one thing stronger. The solar then delivered.
The May 2024 “Gannon” storm was the first excessive occasion of Cycle 25 and the largest geomagnetic storm in additional than 20 years. Its maximum modelled geomagnetically induced present in the UK — 68 amps at the Landulph substation in Cornwall — was recorded by the British Geological Survey. Auroras have been extensively seen throughout the continental United States, Europe, and as far south as Mexico. NOAA has continued issuing geomagnetic storm warnings by the present maximum, with X-class flares triggering radio blackouts and mid-latitude aurora alerts.
2026 might ship one other robust 12 months for Northern Lights shows as Cycle 25 works by its declining part — exactly the window during which the switch-off signature is anticipated to seem.
The sunclock behind the discovery
The switch-off discovering builds on Chapman’s earlier “sunclock” concept, which makes use of a Hilbert rework of the sunspot file to map the solar’s irregular cycles onto a standardized clock face. Because no two solar cycles run the identical size — some stretch previous 12 years, others contract to 9 — evaluating them straight is tough. The sunclock normalizes time, letting researchers overlay cycles and see recurring options.
When cycles are stacked on the sunclock, the abrupt cessation of excessive occasions strains up at a constant part. That regularity is what permits the sunspot count at the switch-off to carry predictive details about the next cycle. A follow-up paper in Frontiers in Astronomy and Space Sciences confirmed the switch-off will be estimated straight from the uncooked sunspot time sequence, with out the edge results of the Hilbert rework.
The underlying physics has now been sharpened. Chapman’s crew argues that the excessive storms are powered by differential rotation twisting the rising magnetic subject, and that this driver shuts down as soon as lively areas cross into the equatorial band the place the solar rotates as a practically inflexible physique. That is the mechanism doing the switching.
Forecasting as infrastructure
Space weather forecasting has quietly grow to be essential infrastructure. GPS accuracy, transoceanic aviation routes, satellite tv for pc lifetimes, and grid stability all rely on understanding what the solar is about to do. The hole between the present era of forecasts and the lead instances wanted for main hardening choices has been one of the subject’s power frustrations.
A way that pushes dependable prediction out to seven years — if it holds by impartial testing on future cycles — would reshape how operators plan. It would additionally shift some of the threat dialog from reactive scrambling throughout a storm to proactive engineering throughout quiet durations.
The approach nonetheless wants validation throughout a number of cycles before it turns into an operational device. Cycle 25’s switch-off, anticipated round 2028 on Chapman’s present estimate, can be the essential check.
What to watch
Three issues will decide whether or not the switch-off methodology graduates from promising to operational.
First, the timing of Cycle 25’s precise switch-off level. Chapman’s present estimate locations it roughly two years out. If excessive occasions taper on schedule, the bodily mannequin good points credibility.
Second, the sunspot count at that second. That quantity, run by the correlation, will yield a agency prediction for Cycle 26’s peak. Comparing it in opposition to different forecasting strategies — polar subject observations, machine studying fashions, dynamo simulations — will present whether or not switch-off outperforms.
Third, the bodily mechanism. A prediction that works empirically however lacks a causal rationalization is fragile. The differential-rotation-and-15-degree-band argument provides switch-off a candidate mechanism; testing it in opposition to the next few cycles will present whether or not it holds up.
For now, the solar is doing what suns do — pumping out flares, flipping its magnetic subject, and dragging the terrestrial electromagnetic atmosphere together with it. The distinction is that a small group of physicists in Coventry consider they’ve discovered the second the place the star suggestions its hand about what comes next.
