Solar
Cycle 25 peaking around 2022 could be one of the weakest
in centuries.
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May
10, 2006: The Sun's Great Conveyor Belt has slowed
to a record-low crawl, according to research by NASA solar
physicist David Hathaway. "It's off the bottom of the
charts," he says. "This has important repercussions
for future solar activity."
The
Great Conveyor Belt is a massive circulating current of fire
(hot plasma) within the Sun. It has two branches, north and
south, each taking about 40 years to perform one complete
circuit. Researchers believe the turning of the belt controls
the sunspot cycle, and that's why the slowdown is important.
Right:
The sun's "Great Conveyor Belt" in profile.
"Normally,
the conveyor belt moves about 1 meter per second—walking pace,"
says Hathaway. "That's how it has been since the late
19th century." In recent years, however, the belt has
decelerated to 0.75 m/s in the north and 0.35 m/s in the south.
"We've never seen speeds so low."
According
to theory and observation, the speed of the belt foretells
the intensity of sunspot activity ~20 years in the future.
A slow belt means lower solar activity; a fast belt means
stronger activity. The reasons for this are explained in the
Science@NASA story Solar
Storm Warning.
"The
slowdown we see now means that Solar Cycle 25, peaking around
the year 2022, could be one of the weakest in centuries,"
says Hathaway.
This
is interesting news for astronauts. Solar Cycle 25 is when
the Vision for Space Exploration should be in full flower,
with men and women back on the Moon preparing to go to Mars.
A weak solar cycle means they won't have to worry so much
about solar flares and radiation storms.
![see caption](images/longrange/predictions3_strip.jpg)
Above:
In red, David Hathaway's predictions for the next two solar
cycles and, in pink, Mausumi Dikpati's prediction for cycle
24.
On
the other hand, they will have to worry more about cosmic
rays. Cosmic rays are high-energy particles from deep space;
they penetrate metal, plastic, flesh and bone. Astronauts
exposed to cosmic rays develop an increased risk of cancer,
cataracts and other maladies. Ironically, solar explosions,
which produce their own deadly radiation, sweep away the even
deadlier cosmic rays. As flares subside, cosmic rays intensify—yin,
yang.
Hathaway's
prediction should not be confused with another recent forecast:
A team led by physicist Mausumi Dikpata of NCAR has predicted
that Cycle 24, peaking in 2011 or 2012, will be intense. Hathaway
agrees: "Cycle 24 will be strong. Cycle 25 will be weak.
Both of these predictions are based on the observed behavior
of the conveyor belt."
How
do you observe a belt that plunges 200,000 km below the surface
of the sun?
"We
do it using sunspots," Hathaway explains. Sunspots are
magnetic knots that bubble up from the base of the conveyor
belt, eventually popping through the surface of the sun. Astronomers
have long known that sunspots have a tendency to drift—from
mid solar latitudes toward the sun's equator. According to
current thinking, this drift is caused by the motion of the
conveyor belt. "By measuring the drift of sunspot groups,"
says Hathaway, "we indirectly measure the speed of the
belt."
Right:
Hathaway monitors the speed of the Conveyor Belt by plotting
the drift of sunspot groups from high to low solar latitude.
This plot is called "the Butterfly Diagram." The
tilt of the wings reveal the speed of the Conveyor Belt. [More]
Using
historical sunspot records, Hathaway has succeeded in clocking
the conveyor belt as far back as 1890. The numbers are compelling:
For more than a century, "the speed of the belt has been
a good predictor of future solar activity."
If
the trend holds, Solar Cycle 25 in 2022 could be, like the
belt itself, "off the bottom of the charts."
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Author: Dr. Tony
Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
More
Information |
Who's
Afraid of a Solar Flare? -- (Science@NASA) Solar
activity can be surprisingly good for astronauts.
A
word about solar cycles: Astronomers number
each 11-year solar cycle, 1, 2, 3 and so on. For obscure
historical reasons, Solar Cycle 1 is a nondescript cycle
which peaked in 1760. The most recent cycle, Cycle 23,
peaked in 2001 and is coming to an end now. Hathaway's
prediction concerns Cycle 25. "The speed of the
conveyor belt predicts solar activity two cycles ahead,"
he explains. "The belt was moving slowly during
Cycle 23; that means Cycle 25 will be weak."
Solar
Storm Warning -- (Science@NASA) Solar Cycle 24 should
be intense
Scientists
Issue Unprecedented Forecast of Next Sunspot Cycle
-- NCAR press release.
The
Vision for Space Exploration |
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