The Early Decline of Solar Cycle 25
The Early Decline of Solar Cycle 25
What changes first and why amateurs often notice it before the models do
Solar cycles do not end with a bang. They fade.
After the excitement of solar maximum - lively higher HF bands, frequent openings, and a sense that “everything is possible” the decline phase begins quietly. There is no clear date when the cycle turns. Instead, small changes creep in, often noticed first by operators who spend time listening rather than watching indices.
Using CW Reverse Beacon spot data covering late August 2024 through December 2025, this article looks at how the early decline of Solar Cycle 25 reveals itself on the HF bands, which changes appear first, and why amateur observations frequently detect them before formal models or forecasts catch up.
Decline is not the opposite of ascent
It is tempting to think of the solar cycle as symmetrical: what improved on the way up should simply reverse on the way down. In reality, the decline phase behaves quite differently.
On the way up:
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ionisation increases steadily,
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the MUF rises,
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higher bands appear more often and for longer.
On the way down:
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ionisation remains high for a long time,
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but stability begins to erode,
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and marginal propagation becomes less reliable.
The first signs of decline are therefore not dramatic losses, but subtle changes in consistency.
What changes first: reliability, not peak performance
One of the clearest early signals in the RBN data is not a collapse in maximum capability, but a change in how often that capability appears.
In practical terms:
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10m still opens, but on fewer days
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openings start later and end earlier
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day-to-day variability increases
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strong outlier days remain, but become isolated
This is an important distinction. Solar flux can remain high, and sunspot numbers can still look impressive, while usable propagation becomes less dependable.
High bands show the earliest decline signatures
The earliest and clearest signs of solar-cycle decline appear at the top of the HF spectrum.
The RBN data reveals that:
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10m and 12m show increasing gaps between active days
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sequences of consecutive good days shorten
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openings become more sensitive to geomagnetic and seasonal effects
This makes sense physically. These bands operate closest to the MUF, so even small reductions in peak ionisation, or small increases in instability, remove support.
Crucially, this happens before there is any obvious change in average solar indices.
The “ladder” still exists - but loses rungs
Earlier in the cycle, MUF behaviour often resembles a smooth ladder:
15m → 12m →10 m, day after day.
During early decline, that ladder becomes irregular:
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15m remains reliable
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12m appears intermittently
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10m becomes opportunistic rather than expected
The MUF still rises during the day, but it reaches the highest rungs less often and for shorter periods. This is exactly the kind of behaviour that long-running RBN observations reveal clearly, but which is easy to miss in casual operating.
Why 20m and 17m change later - and more subtly
Mid-HF bands such as 20m and 17m behave very differently during early decline.
The data shows that:
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spot counts remain broadly stable
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time-of-day structure changes very little
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seasonal effects dominate over solar-cycle effects
This often leads to the impression that nothing has changed, especially for operators who spend most of their time on 20m.
In reality, these bands are simply buffered:
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they operate well below the MUF
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they tolerate modest reductions in ionisation
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they are less sensitive to small increases in instability
As a result, they are poor early-warning indicators, but excellent baselines.
Lower bands barely notice - at first
On 40m (and below), early solar-cycle decline is almost invisible.
The data indicates that:
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40m spot counts remain strong
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evening and night-time performance changes little
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seasonal and geomagnetic effects dominate behaviour
This reinforces an important point: solar-cycle decline does not arrive from below, it arrives from above
By the time lower bands show obvious solar-cycle effects, the higher bands have often been changing for months.
Why amateurs often notice decline before the models do
This raises an interesting question: why do amateurs frequently sense the decline before formal predictions acknowledge it?
There are several reasons.
1. Models focus on averages
Forecasts track smoothed indices such as F10.7 and sunspot number. They are designed to describe the cycle, not the experience.
2. Operators notice reliability
Amateurs notice when:
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openings fail to repeat
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schedules become harder to keep
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“expected” bands don’t deliver
These are second-order effects that do not show up immediately in averaged data.
3. RBN and WSPR expose marginal behaviour
Weak-signal networks are extremely sensitive to changes at the margin. They reveal when propagation is still possible but no longer dependable - the hallmark of early decline.
Decline does not mean worse everywhere
It is important to stress that early decline does not mean poor HF conditions.
In many respects:
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20m remains excellent
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17m can feel unchanged
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15m often continues to perform well
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low bands benefit from reduced absorption as activity slowly eases
What changes is not overall capability, but distribution and predictability.
From a scientific perspective, it is also one of the most informative phases of the cycle, because small changes are easier to detect than gross trends.
Solar Cycle 25 will not end abruptly. It will taper, unevenly and sometimes confusingly. The first signs are not dramatic collapses, but subtle losses of reliability at the top of the HF spectrum.The RBN data shows that amateur observations are not merely anecdotal - they are often early indicators of changing ionospheric behaviour. Long before the models redraw their curves, the bands themselves begin to tell the story.
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