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The Solar Cycle
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Credit: NASA
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NASA
Aids in Resolving Long Standing Solar Cycle Mystery
Scientists
predict the next solar activity cycle will be 30 to 50 percent
stronger than the previous one and up to a year late. Accurately
predicting the sun's cycles will help plan for the effects of
solar storms. The storms can disrupt satellite orbits and
electronics; interfere with radio communication; damage power
systems; and can be hazardous to unprotected astronauts.
The breakthrough
"solar climate" forecast by Mausumi Dikpati and
colleagues at the National Center for Atmospheric Research in
Boulder, Colo. was made with a combination of computer simulation
and groundbreaking observations of the solar interior from space
using NASA's Solar and Heliospheric Observatory (SOHO). NASA's
Living With a Star program and the National Science Foundation
funded the research.
The sun goes through a roughly
11-year cycle of activity, from stormy to quiet and back again.
Solar storms begin with tangled magnetic fields generated by the
sun's churning electrically charged gas (plasma). Like a rubber
band twisted too far, solar magnetic fields can suddenly snap to
a new shape, releasing tremendous energy as a flare or a coronal
mass ejection (CME). This violent solar activity often occurs
near sunspots, dark regions on the sun caused by concentrated
magnetic fields.
Understanding plasma flows in the sun's
interior is essential to predicting the solar activity cycle.
Plasma currents within the sun transport, concentrate, and help
dissipate solar magnetic fields. "We understood these flows
in a general way, but the details were unclear, so we could not
use them to make predictions before," Dikpati said. Her
paper about this research was published in the March 3 online
edition of Geophysical Research Letters.
The new
technique of "helioseismology" revealed these details
by allowing researchers to see inside the sun. Helioseismology
traces sound waves reverberating inside the sun to build up a
picture of the interior, similar to the way an ultrasound scan is
used to create a picture of an unborn baby.
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Credit: NASA
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Two major plasma flows
govern the cycle. The first acts like a conveyor belt. Deep
beneath the surface, plasma flows from the poles to the equator.
At the equator, the plasma rises and flows back to the poles,
where it sinks and repeats. The second flow acts like a taffy
pull. The surface layer of the sun rotates faster at the equator
than it does near the poles. Since the large-scale solar magnetic
field crosses the equator as it goes from pole to pole, it gets
wrapped around the equator, over and over again, by the faster
rotation there. This is what periodically concentrates the solar
magnetic field, leading to peaks in solar storm activity.
"Precise helioseismic observations of the 'conveyor
belt' flow speed by the Michelson Doppler Imager (MDI) instrument
on board SOHO gave us a breakthrough," Dikpati said. "We
now know it takes two cycles to fill half the belt with magnetic
field and another two cycles to fill the other half. Because of
this, the next solar cycle depends on characteristics from as far
back as 40 years previously - the sun has a magnetic 'memory'."
The magnetic data input comes from the SOHO/MDI
instrument and historical records. Computer analysis of the past
eight years' magnetic data matched actual observations over the
last 80 years. The team added magnetic data and ran the model
ahead 10 years to get their prediction for the next cycle. The
sun is in the quiet period for the current cycle (cycle 23).
The team predicts the next cycle will begin with an
increase in solar activity in late 2007 or early 2008, and there
will be 30 to 50 percent more sunspots, flares, and CMEs in cycle
24. This is about one year later than the prediction using
previous methods, which rely on such statistics as the strength
of the large-scale solar magnetic field and the number of
sunspots to make estimates for the next cycle. This work will be
advanced by more detail observations from the Solar Dynamics
Observatory, scheduled to launch in August 2008.
SOHO Spacecraft
5.7 Mb - no audio
Credit: NASA
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Each image has a hot spot to
the following video's
1.SEP At Earth
2.Solar Magnetism
3.CME Explosion
4.Solar Region Formation
5.CME Reconnection
6.TRACE Flare 1
All Video's are MPG
Credit: NASA
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SOHO
is a project of international collaboration between NASA and the
European Space Agency.
Source
/ Credit: NASA
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