A new
computer model which accurately simulates the Sun's past few solar cycles
predicts that the next cycle will be up to 50 percent stronger than its
predecessor and begin a year later than expected, scientists announced Monday.
The National Center for Atmospheric Research's (NCAR)
Mausumi Dikpati and colleagues developed the model, which is detailed in the
March 3 issue of Geophysical Research Letters, and announced their
findings in a press conference today.
The model offers
a possible solution to the 150-year-old mystery of what's behind the Sun's
approximately 11-year cycle of activity. It could also lead to better planning
for space weather, such as solar flares and coronal mass ejections, which can
disrupt navigation and power systems and threaten
astronauts in space.
The next
cycle
The Sun
goes through approximately 11-year cycles that range from peak activity to
quiet and back again. We are near the low point of the current cycle.
Scientists
have tracked the cycles for decades but have been unable to predict when their
durations and intensity.
The new
model, known as the Predictive Flux-transport Dynamo Model, has simulated the
strength of the past eight solar cycles extending back to the early 1900s with
98 percent accuracy.
Using the
model, researchers predict that the next solar cycle, known as Cycle 24, will
produce sunspots across an area slightly larger than 2.5 percent of the visible
surface of the Sun. They also expect that the cycle will begin in late 2007 or
early 2008--about six to 12 months later than earlier predictions--and reach its
peak in 2012.
The
researchers attribute the accuracy of the new model to recent observations of
how currents of electrical gas called plasma circulate between the Sun's
equator and its pole, and how these currents are affected by the Sun's
rotation.
Birth of
a sunspot
The birth
of a new sunspot begins with the death of an old one from a previous cycle. As
an old sunspot decays, it leaves a magnetic "imprint" or signature on the flow
of plasma moving between the Sun's equator and its poles.
As the
plasma current approaches the poles, it sinks about 124,000 miles (200,000
kilometers) down into the Sun's interior and starts its return journey back to
the equator.
These
subsurface plasma flows have been verified with observations from NASA's Solar
and Heliospheric Observatory (SOHO),
which uses sound waves inside the Sun to reveal details about its interior.
Observations
show that as the plasma currents move, they are affected by the Sun's rotation.
Unlike the Earth, the Sun's equator moves more rapidly than its poles.
This
differential rotation stretches and twists the moving plasma current, making it
more unstable than surrounding plasma. Eventually, the warped plasma currents
rise up and tear through the Sun's surface, creating a new sunspot. When the new
sunspots begin to decay, the cycle begins anew.
Positive
reception
David
Hathaway, a NASA solar astronomer who was not involved in the study, said he is
excited about the new model.
"It's based
on sound physical principals and it finally answers the 150-year-old question
of what causes the 11-year sun spot cycle," Hathaway said.
Hathaway's
team agrees with Dikpati that Cycle 24 will be stronger than the last one, but
disputes the claim that it will occur later than expected.
After
reviewing the previous 12 solar cycles, Hathaway's team believes large cycles
usually start early and that Cycle 24 will start sometime later this year or
early next year.
The new
predictions could mean that Earth could experience more intense solar flares
and related space
weather in upcoming years.
"This
prediction suggests we're potentially looking at more communications and
navigation disruptions, more satellite failures, possible disruptions of
electrical grids and blackouts and more dangerous conditions for astronauts,"
said Richard Behnke, program director of the National Science Foundation's
division of atmospheric sciences, which funded the research.
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