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effects they produce, according to the
study’s authors.
NCAR deputy director Scott
McIntosh, a solar physicist who led the
study, said: “Scientists have struggled
to predict both the length and the
strength of sunspot cycles because we
lack a fundamental understanding of
the mechanism that drives the cycle.
If our forecast proves correct, we will
have evidence that our framework
for understanding the sun’s internal
magnetic machine is on the right path”.
In McIntosh’s previous work,
he and his colleagues sketched the
outline of a 22 year extended solar
cycle using observations of coronal
bright points, ephemeral flickers of
extreme ultraviolet light in the solar
atmosphere. These bright points can Study co-author Bob Leamon, a researcher at the University of Maryland, Baltimore
be seen marching from the sun’s high County added: “When we look back over the 270-year long observational record of
latitudes to the equator over about 20 terminator events, we see that the longer the time between terminators, the weaker the
years. As they cross the mid-latitudes, next cycle. Conversely, the shorter the time between terminators, the stronger the next
the bright points coincide with the solar cycle is.
emergence of sunspot activity. This correlation has been difficult for scientists to see in the past because they
McIntosh believes the bright points have traditionally measured the length of a sunspot cycle from solar minimum to solar
mark the travel of magnetic field bands minimum, which is defined using an average rather than a precise event. In the new
which wrap around the sun. When the study, the researchers measured from terminator to terminator, which allows for much
bands from the northern and southern greater precision.
hemispheres – which have oppositely While terminator events occur approximately every 11 years and mark the beginning
charged magnetic fields – meet at the and end of the sunspot cycle, the time between terminators can vary by years. For
equator, they mutually annihilate one example, Sunspot Cycle 4 began with a terminator in 1786 and ended with a terminator in
another, leading to a “terminator” event. 1801, an unprecedented 15 years later. The following cycle, five, was incredibly weak with
These terminators are crucial markers on a peak amplitude of just 82 sunspots. That cycle would become known as the beginning of
the sun’s 22 year clock, McIntosh says, the Dalton Grand Minimum.
because they flag the end of a magnetic Similarly, Sunspot Cycle 23 began in 1998 and did not end until 2011, 13 years later.
cycle, along with its corresponding Sunspot Cycle 24, which is just ending, was quite weak as well but it was also quite short
sunspot cycle, and act as a trigger for the – just shy of ten years long – and that’s the basis for the new study’s bullish prediction
following magnetic cycle to begin. that Sunspot Cycle 25 will be strong”.
While one set of oppositely charged McIntosh said: “Once you identify the terminators in the historical records, the pattern
bands is about halfway through its becomes obvious. A weak Sunspot Cycle 25, as the community is predicting, would be a
migration toward the equatorial meetup, complete departure from everything that the data has shown us up to this point”.
a second set appears at high latitudes Bottom line: scientists led by the National Centre for Atmospheric Research say
and begins its own migration. While their study of oppositely charged magnetic field bands, moving in the sun’s northern and
these bands appear at high latitudes at southern hemispheres, suggests that the coming Sunspot cycle – Cycle 25 – will be a
a relatively consistent rate – every 11 particularly strong one. This result is in direct contradiction to an earlier expert forecast,
years – they sometimes slow as they suggesting Cycle 25 (like Cycle 24) would produce fewer than usual sunspots. n
cross the mid-latitudes, which appears
to weaken the strength of the upcoming
solar cycle.
This happens because the slowdown National Centre for Atmospheric
acts to increase the amount of time that Research (NCAR)
the oppositely charged sets of bands
overlap and interfere with one another NCAR was established by the National Science Foundation in 1960 to provide the
inside the sun. The slowdown extends
US university community with world-class facilities and services that were beyond
the current solar cycle by pushing the the reach of any individual institution. More than a half-century later, they are still
terminator event out in time. Shifting the delivering on that mission. NCAR provides the atmospheric and related Earth system
terminator out in time has the effect of science community with state-of-the-art resources including super-computers, research
eating away at the spot productivity of the aircraft, sophisticated computer models and extensive data sets.
next cycle.

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