A long-running study using the Birmingham Solar-Oscillations Network found that the Sun’s internal acoustic waves have been carrying signals that diverge from standard surface measures, including sunspot counts and 10.7-centimetre radio flux. The shift appears across Solar Cycles 22 to 25, covering observations from 1987 to 2025, and suggests that key structural changes linked to magnetic activity have moved closer to the outer layers of the Sun.
Researchers found that Solar Cycle 25 looks weaker than earlier cycles when judged by conventional global activity proxies, but appears comparable to Cycles 22 and 23 when viewed through higher-frequency seismic bands. That mismatch is central to the study’s significance: the Sun may be changing internally in ways that cannot be captured by counting sunspots alone.
Helioseismology works by measuring pressure waves, or p modes, that travel through the solar interior and subtly shift as magnetic fields alter the structure through which they pass. Lower-frequency modes probe deeper layers, while higher-frequency modes are more sensitive to regions closer to the surface. The latest findings show stronger-than-expected frequency shifts in high-frequency modes, while mid-frequency modes have become less responsive to activity over successive cycles.
That pattern points to magnetic activity being increasingly concentrated in a shallower subsurface layer, possibly within about 1,000 kilometres of the Sun’s visible surface. Such a change would not necessarily produce an obvious jump in sunspot numbers, yet it could affect how magnetic energy builds, reorganises and erupts into space.
Space-weather forecasting depends heavily on surface-facing indicators because they are easier to observe continuously. Sunspots, active regions, radio flux and magnetic-field maps are used to estimate the likelihood of solar flares, coronal mass ejections and geomagnetic storms. These events can disrupt satellites, aviation communication, navigation systems, power grids and high-frequency radio networks.
The new evidence does not mean forecasts are wrong in all cases, nor does it show that the Sun is becoming more dangerous. It does, however, suggest that models calibrated against surface behaviour may be missing a structural trend beneath the photosphere. If magnetic activity is being stored or redistributed differently, forecasts based only on visible activity could underestimate or misread the physical state of the solar cycle.
Solar Cycle 25 began in December 2019 and reached its maximum phase after a stronger-than-expected rise in activity. The cycle produced major flares and geomagnetic storms, including events that drove auroral displays far beyond polar regions. Yet its overall sunspot-based strength remains below the largest cycles of the late 20th century, making the seismic signal especially notable.
The study also revives a long-running debate about the solar dynamo, the mechanism that generates and organises the Sun’s magnetic field. Traditional explanations place much of the dynamo’s organising power deep in the solar interior, near the tachocline, where the radiative and convective zones meet. Other work has argued that near-surface processes may play a larger role than once assumed. The new helioseismic evidence does not settle that debate, but it adds pressure to account for layered magnetic behaviour rather than treating the cycle as a single surface-visible rhythm.
The research team includes William J. Chaplin, Sarbani Basu, Rachel Howe, Yvonne Elsworth, Steven J. Hale and Eleanor Murray. Their analysis builds on earlier findings that the relationship between seismic frequency shifts and activity proxies changed during the declining phase of Solar Cycle 23, then persisted through Cycle 24. Cycle 25 data now show that the trend is not a one-cycle anomaly.
BiSON’s importance lies in its duration. The ground-based network has tracked the Sun as a star for decades, providing a continuous record long enough to compare successive cycles. Without that span, shifts in the relationship between internal oscillations and surface activity would be difficult to separate from shorter-term variation.
Scientists are likely to test the finding against other helioseismic records and space-based observations from instruments that monitor solar oscillations, magnetic fields and extreme ultraviolet emissions. Independent confirmation would strengthen the case for recalibrating solar-cycle models to include seismic indicators that reveal subsurface changes before they emerge in visible activity.
Follow Arabian Post
Select Arabian Post as your preferred source on Google and MSN News for trusted business news and Arab politics and updates.
