2012: Super Sunspot Cycle Peak! |
Increasing sunspot activity was clearly visible as
our star approached its latest maximum, in 1999.
The next 11-year sunspot cycle will be late but strong
according to a new computer prediction. The model used
was virtually spot on when applied retrospectively to
"forecast" the last eight solar cycles.
"We predict the next cycle will be 30% to 50% stronger
than the last cycle," says the model's creator,
Mausumi Dikpati, of the National
Center for Atmospheric Research's High Altitude Observatory
in Boulder, Colorado, US.
The Sun is currently near its minimum activity, at the
tail end of a solar cycle, numbered 23. "Onset
of the next cycle will be delayed by six to 12 months,
to late 2007 or early 2008," Dikpati
says. She expects the next peak to hit in 2012.
Although each solar cycle – from sunspot minimum
to maximum and back again – is roughly 11 years,
the periods can vary in length and intensity. The factors
governing the cycle have been largely inscrutable.
Dikpati's team tackled the
problem by incorporating updated solar dynamical theories
along with observations of the Sun dating back to 1880.
The result is a model of the Sun with a 20-year "memory"
of its magnetic field activity.
Image: SOHO/NASA/ESA
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Coronal ejections |
The model can be tested using past data to "predict"
the nature of cycles that have in fact already occurred
– and it describes cycles 16 to 23 with better
than 97% accuracy. If the model proves to make accurate
real predictions, it will finally answer the 150-year-old
question of what causes the sunspot cycle, said David
Hathaway, a solar astronomer at NASA's Marshall
Space Flight Center in Huntsville, Alabama, US, during
a press conference on Monday.
And understanding the solar cycle is not just important
for science. If the magnetic field lines that pop up
to the Sun's surface as a sunspot are twisted and rotate,
the spot can yield solar flares and coronal mass ejections,
which spew radiation and charged particles in Earth's
direction.
Such storms can disrupt the Earth's upper atmosphere,
causing numerous problems. So knowing when a cycle is
likely to peak could be particularly important during
a strong sunspot cycle, says Richard
Behnke, director of the US National Science Foundation's
Upper Atmospheric Research Section.
"This prediction suggests we're potentially looking
at more communications and navigations disruptions,
more satellite failures, possible disruptions of electrical
grids, blackouts, and more dangerous conditions for
astronauts," he says.
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Spot the difference |
The new results contradict those of a model published
in 2005 that found the next cycle could be the weakest
in 100 years. Leif Svalgaard,
a member of the team behind that model, says the key
difference boils down to one simple thing: "How
long does the Sun remember its magnetic field?"
Both models are based on the idea that the movement
of the Sun's spots is driven by a current of plasma,
which pushes the remnants of spots toward the poles,
where they sink.
But Svalgaard's model assumes
the polar fields left over as one cycle declines then
seed the sunspots of the next cycle – i.e. the
field strengths from the last cycle directly indicate
the strength of the sunspots during the next solar cycle.
"We think the Sun forgets its magnetic memory,"
Svalgaard told New
Scientist.
In Dikpati's new model, a
sunspot's remnants are carried poleward and down to
a depth of about 200,000 kilometres by a plasma "conveyor
belt" over a span of about 20 years. They are then
carried by a slow flow back toward the equator, and
eventually surface as sunspots once again.
This means the strength of the next cycle would depend
on the strength of the polar fields from the last three
cycles. Cycles 21 and 22 were relatively strong, while
cycle 23 was weak, so Dikpati's
model predicts the next cycle will be stronger, while
Svalgaard's suggests it will
be weaker.
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Watching and waiting |
"It's good the models are diverging," Svalgaard
says. "If all models predict the same thing, we
don't get wiser." Which model is right will become
clear in the first few years of the next solar cycle.
"We're all waiting," he says.
Dikpati's model looks excellent
based on the tests on previous cycles, but while Hathaway's
group at NASA's Marshall Space Flight Center agrees
with the prediction of a strong next cycle, they disagree
about a delayed onset.
Based on the last 12 cycles, "large cycles usually
start early", she told New Scientist. She expects
the cycle to begin in late 2006 or early 2007: "We're
anxiously awaiting the appearance of those first spots
in the new cycle."
Journal Reference: Geophysical Research
Letters (vol 33, L05102)
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Patrick Geryl © 2005 ~ 2008 / site by kAOz :: happyland |
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