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Dec. 21, 2006: Evidence is mounting: the next solar
cycle is going to be a big one.
Solar
cycle 24, due to peak in 2010 or 2011 "looks like its going
to be one of the most intense cycles since record-keeping began
almost 400 years ago," says solar physicist David Hathaway
of the Marshall Space Flight Center. He and colleague Robert
Wilson presented this conclusion last week at the American Geophysical
Union meeting in San Francisco.
Right:
An erupting solar prominence photographed by the Solar and
Heliospheric Observatory (SOHO). [More]
Their
forecast is based on historical records of geomagnetic storms.
Hathaway
explains: "When a gust of solar wind hits Earth's magnetic
field, the impact causes the magnetic field to shake. If it
shakes hard enough, we call it a geomagnetic storm."
In the extreme, these storms cause power outages and make
compass needles swing in the wrong direction. Auroras are
a beautiful side-effect.
Hathaway
and Wilson looked at records of geomagnetic activity stretching
back almost 150 years and noticed something useful:. "The
amount of geomagnetic activity now tells us what the solar
cycle is going to be like 6 to 8 years in the future,"
says Hathaway. A picture is worth a thousand words:
Above:
Peaks in geomagnetic activity (red) foretell solar maxima
(black) more than six years in advance. [More]
In
the plot, above, black curves are solar cycles; the amplitude
is the sunspot number. Red curves are geomagnetic indices,
specifically the Inter-hour Variability Index or IHV. "These
indices are derived from magnetometer data recorded at two
points on opposite sides of Earth: one in England and another
in Australia. IHV data have been taken every day since 1868,"
says Hathaway.
Cross
correlating sunspot number vs. IHV, they found that the IHV
predicts the amplitude of the solar cycle 6-plus years in
advance with a 94% correlation coefficient.
"We
don't know why this works," says Hathaway. The underlying
physics is a mystery. "But it does work."
According
to their analysis, the next Solar Maximum should peak around
2010 with a sunspot number of 160 plus or minus 25. This would
make it one of the strongest solar cycles of the past fifty
years—which is to say, one of the strongest in recorded history.
Left:
Hathaway and Wilson's prediction for the amplitude of Solar
Cycle 24. [More]
Astronomers
have been counting sunspots since the days of Galileo, watching
solar activity rise and fall every 11 years. Curiously, four
of the five biggest cycles on record have come in the past
50 years. "Cycle 24 should fit right into that pattern,"
says Hathaway.
These
results are just the latest signs pointing to a big Cycle
24. Most compelling of all, believes Hathaway, is the work
of Mausumi Dikpati and colleagues at the National Center for
Atmospheric Research (NCAR) in Boulder, Colorado. "They
have combined observations of the sun’s 'Great Conveyor Belt'
with a sophisticated computer model of the sun’s inner dynamo
to produce a physics-based prediction of the next solar cycle."
In short, it's going to be intense. Details may be found in
the Science@NASA story Solar
Storm Warning.
"It
all hangs together," says Hathaway. Stay tuned for solar
activity.
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Author: Dr. Tony
Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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Hathaway
points out that there are actually two types of geomagnetic
activity:
(1)
storms caused by the gentle buffeting of solar wind
streams and
(2)
storms caused by the more forceful impact of flares
and coronal mass ejections (CMEs).
"Only
the first type has predictive value," says Hathaway.
"Storms caused by solar wind streams come and go
in a regular pattern that foretells the solar cycle.
Storms caused by flares and CMEs don't have this property."
To improve their results, Hathaway and Wilson used a
technique developed by Joan Feynman to remove storms
caused by flares and CMEs from their data.
Reference:
Hathaway, D. H. and Wilson, R. M. 2006, "Geomagnetic
activity indicates large amplitude for sunspot cycle
24", Geophys. Res. Lett. in press.
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