Page 28 - EngineerIT August-September 2025

SCIENCE

Next solar cycle could be more

intense as the Glassberg wakes up

By Hans van de Groenendaal, Science and technology writer

Readers of EngineerIT may be acquainted with the 11-year solar cycle that impacts on radio
communication and the production and intensity of solar flares and coronal mass ejections
(CMEs) but for many the centennial cycle is relatively an unknown phenomenon

he next few solar cycles could be even That's exactly what Adams found in his research. The protons are
more intense; the resultant of a little- clearly decreasing in measurements obtained from NOAA's Polar
Tknown phenomenon called the "Centennial Operational Environmental Satellites.
Gleissberg Cycle."
Protons in the South Atlantic Anomaly are just the latest in a
The Gleissberg Cycle is a slower modulation, which growing body of evidence suggesting that the "Gleissberg Minimum"
suppresses sunspot numbers every 80 to 100 years. has passed. Current sunspot counts are up; the sun's ultraviolet
For the past ~15 years, the Sun has been near a low output has increased; and the overall level of solar activity in Solar
point in this cycle, but this is about to change. Cycle 25 has exceeded forecasts. It all adds up to an upswing in the
100-year cycle.
New research published in the journal Space
Weather suggests that the Gleissberg Cycle is It also means that Joan Feynman was right. Before she passed away
waking up again. If this is true, solar cycles for the in 2020, the pioneering solar physicist was a leading researcher of
next 50 years could become increasingly intense. the Gleissberg Cycle, and she firmly believed that the centennial
oscillation was responsible for the remarkable weakness of Solar
"We have been looking at protons in the South Cycle 24 (2012-2013). In a seminal paper published in 2014, she
Atlantic Anomaly," explains the paper's lead author argued that the minimum of the Gleissberg Cycle fell almost squarely
Kalvyn Adams, an astrophysics student at the on top of Solar Cycle 24, making it the weakest cycle in 100 years.
University of Colorado. "These are particles from the The tide was about to turn.
Sun that come unusually close to Earth because
our planet's magnetic shield is weak over the south The resurgence of the Gleissberg Cycle makes a clear prediction
Atlantic Ocean." for the future: Solar Cycles 26 through 28 should be progressively
intense. Solar Cycle 26, peaking in ~2036, would be stronger than
The South Atlantic Anomaly is a weak spot in Earth's current Solar Cycle 25, and so on. The projected maximum of the
magnetic field where particles from the Sun can Gleissberg Cycle is around 2055, aligning with Solar Cycle 28.
come relatively close to Earth. That cycle could be quite intense.

It turns out that protons in the South Atlantic Solar flares produce high energy particles and radiation that are
Anomaly are a "canary in a coal mine" for the dangerous to living organisms. However, on the surface of the
Gleissberg Cycle. When these protons decrease, it Earth, we are protected from the effects of solar flares by the Earth's
means the Gleissberg Cycle is about to surge. magnetic field and atmosphere. The most dangerous emissions
from flares are energetic charged particles (primarily high-energy
protons) and electromagnetic radiation (primarily x-rays).

Major geomagnetic storms are induced by coronal mass ejections
(CMEs) which are frequently associated with flares. Like flares, CMEs
are more frequent during the active phase of the Sun's approximately
11-year cycle. The exact relationship between flares and CMEs is still
not well understood, as flares seem to trigger CMEs but sometimes
CMEs are observed without any flares.

CMEs are more likely to have a significant effect than flares because
they carry more material into a larger volume of interplanetary
space, increasing the likelihood that they will interact with the Earth.

28 | EngineerIT August/September 2025