- If the Sun spits, the Earth fries. Humankind
is ill-prepared for the furious climax of the next solar cycle.
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- Batten down the hatches, there's a storm
coming. Some time in the next 18 months, the Sun will turn from a relatively
placid ball of hot ionised gases into a raging tempest of plasma, spitting
fireballs out into the Solar System like an angry god. Woe betide any planet
that gets in its way.
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- Should one of those plasma storms hit
Earth, the impact could be devastating. Each fireball--known as a coronal
mass ejection--is a giant maelstrom of ionised gases at temperatures of
well over a million degrees. But the temperature is the least of Earth's
worries. The plasma will tear through the Earth's magnetic field like wind
through grass. These wildly fluctuating fields can knock out power supplies,
and charged particles from the plasma can fry the electronic components
inside telecommunications satellites, bringing down communications networks
over vast areas. A few scientists and engineers are preparing for the worst
while others, strangely, have chosen to ignore the problem. The wary few
are racing to put in place measures to protect power grids and telecommunications
networks, and have launched sentinels that sit in space between the Earth
and the Sun watching for storm signs. In addition, they are developing
complex computer models to predict which parts of the Earth might be affected.
Others, fearing the worst, are waiting to see what happens to the giant
communications networks that have grown up since the last big solar storm
10 years ago.
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- Scientists have been watching the changing
nature of the Sun for over 200 years and have witnessed these solar rages
every eleven years or so. This will be the 23rd cycle on record and researchers
believe it will be every bit as bad as the last. Six million people in
the Canadian province of Quebec can testify to its effects.
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- The storm struck in the early hours of
13 March 1989. It was not a good night to lose power. The temperature had
dropped to -15 °C and furnaces went quiet as six million Canadians
lost heat and light. After the winter sunrise, subways sat still for lack
of power, traffic lights hung dark and petrol pumps refused to deliver.
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- Later in the day, when public officials
called for an explanation, engineers at Hydro-Quebec, the region's power
generating company, had begun to suspect an unusual culprit. Four days
earlier, a giant bubble of plasma had burst from the surface of Sun. That
morning it had hit the Earth, wreaking havoc.
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- Rapidly changing magnetic fields generate
currents in any conductors within reach. This is how a dynamo works--except
that the magnetic field remains still in these devices while the conducting
wires move through it. When a magnetic storm hits the Earth, any networks
of conductors that stretch over the same scale as the magnetic fluctuations
act like giant dynamos. Hydro-Quebec's transmission lines stretch for over
1000 kilometres. Power lines, telephone lines and even railway lines are
all potential conduits for "geomagnetically induced currents"
(GICs) of hundreds of amperes.
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- Power companies are vulnerable because
their power lines guide the GICs towards sensitive components such as transformers
at power stations and substations. A transformer changes a high voltage
supply of alternating current into a low voltage supply or vice versa.
It consists of a giant doughnut of iron with two sets of windings on each
side of the structure. The voltage in one set of windings induces a magnetic
field in the iron core, which in turn induces a voltage in the second set
of windings. The ratio of the number of windings in the two coils determines
the change in voltage.
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- High-performance transformers are delicate
machines. They are designed to cope with voltages within a specific range
of amplitudes and frequencies. Outside these bounds, the transformer behaves
unpredictably.
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- The trouble with GICs is that the voltages
associated with them change this delicate balance. In particular, they
set up voltages at harmonic frequencies to the ordinary load. These frequencies
are transformed but in a way that can rapidly spiral out of control. The
result is wildly fluctuating voltages called voltage asymmetries. If the
power is not shut down, these can create enough heat to damage the iron
core beyond repair. Worse, these fluctuations pass rapidly through the
network so that neighbouring transformers also become affected. Within
seconds an entire network can collapse as one transformer after another
fails.
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- Exactly this happened to Hydro-Quebec's
power system that fateful morning. "Voltage regulations need to be
within 5 to 10 per cent of a nominal value. If you fall outside that, you
generally see a system collapse and the start of a domino effect,"
says John Kappenman, an expert in the effects of geomagnetic storms at
the Metatech Corporation, based in Goleta, California.
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- Many other electricity utilities around
the world also suffered the effects of GICs that morning. Further south,
the iron core of a transformer at a New Jersey power station burnt out
and had to be replaced at a cost of several million dollars. Later, researchers
at the Oak Ridge National Laboratory in Tennessee predicted the potential
effects of a geomagnetic storm only slightly more severe than the one in
1989. They concluded that the ensuing blackouts and chaos could cost the
US economy up to $6 billion dollars in lost business.
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- Astronomers are forecasting storms just
as big as those in 1989 for the next solar maximum, if not bigger. As the
Sun passes through its 11-year cycle, solar astronomers measure the activity
on its surface by counting the number of sunspots and the number of groups
of sunspots they can see during a predetermined period, usually a month
or a year. Together, these numbers allow them to calculate an index of
solar activity known as the International Sunspot Number. During the solar
minimum, the sunspot number can be as low as 10. In July 1989, during the
last solar maximum, it peaked at 159. And in March 1958, it reached 201,
the highest level ever recorded (see <http://www.newscientist.com/ns/19990227/ns/19990227/diagram.htmlFigure).
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- Cycle 23 "will be one of the largest
on record, and comparable to the last two solar cycles", says a panel
of international experts chaired by Jo Ann Joselyn of the US National Oceanic
and Atmospheric Administration's Space Environment Center in Boulder, Colorado.
They warn that the sunspot number could reach 190, peaking sometime between
June this year and January 2001.
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- Can anything be done to avert disaster?
Leonard Bolduc, a researcher at Hydro-Quebec's Institute of Research in
Electricity of Quebec, who was working on the night of the failure, has
studied the network's breakdown. There is little that Hydro-Quebec can
do to prevent GICs. Instead, Bolduc says the company's strategy is to design
grids that can cope. "Hydro-Quebec has spent a lot of money trying
to understand the phenomena and to evaluate all its equipment during a
GIC storm," he says.
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- Its solution has been to fit its power
lines with capacitors, known as transmission line series capacitors, that
prevent the flow of direct current without affecting alternating current.
The company has spent more than C$1.2 billion fitting the new capacitors.
It has also set up monitoring equipment that spots voltage asymmetries
and warns operators to redistribute the load to other parts of the network,
by bringing online other generators in different areas. "We are confident
that our network could now support such a big storm," says Bolduc.
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- Currents and electrojets
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- Another approach is to predict the severity
of geomagnetic storms before they hit the Earth so that preventive action
can be taken. But this isn't easy. The interaction between the Earth's
magnetic field and the particles in the hot plasma is extremely complex.
Ari Viljanen and Risto Pirjola of the Finnish Meteorological Institute
have been studying this process. They began by modelling the interaction
between plasma from the Sun and the Earth's magnetic field, and the way
this generates currents in ionised regions of the Earth's upper atmosphere.
These currents--called the auroral electrojet--have an electric field associated
with them. The horizontal component of this field at the Earth's surface
together with the conductance of the surface are the crucial factors that
determine the strength of GICs. So Viljanen and Pirjola have had to model
the conductivity too.
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- By combining their models of the auroral
electrojet and the conductivity of the Earth's surface, they have created
a formidable tool. Their overall model produces data that come within 20
per cent of the values of GICs measured in the Finnish power system.
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- The Finnish researchers now want to turn
the model on its head. They say that by using data from GICs in Finland,
their model can throw light on the processes at work in the upper atmosphere.
In effect, they hope to turn the entire Finnish power grid system into
a giant instrument for studying the interaction between the magnetosphere
and the solar wind.
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- Kappenman also has ambitious plans. He
is division manager for Metatech's Applied Power Solutions Division, and
the architect of a new computer model called PowerCast designed to predict
the effects of GICs before they occur. His first customer is National Grid--the
company that operates Britain's power transmission network--which is installing
his system this month.
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- PowerCast uses a model of the interaction
between solar plasma, the magnetosphere and the geology of the Earth's
surface. But it links this to a model of the power grid itself. The National
Grid uses about 900 transformers and PowerCast takes into account all of
them when deciding which might be damaged by impending magnetic storms.
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- The data that PowerCast uses to make
its predictions come from a small observatory called the Advanced Composition
Explorer (ACE), a spacecraft that sits in the solar wind approximately
1.5 million kilometres upstream of Earth at the point where the gravitational
forces from the Earth and the Sun balance one another. ACE measures the
composition of the solar wind and gives roughly one hour's warning of an
impending solar storm.
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- Using these data, PowerCast will give
the National Grid a minute-by-minute update of the threat that GICs pose
to the network. Operators can then take appropriate steps to mitigate the
effects of any impending storm while maintaining the supply. It's a difficult
job, says Kappenman. "Power companies are not like phone companies
where, if it gets too busy, they can give you a busy signal." Metatech
claims that the system works with "reasonable accuracy". Just
how it it will perform during the forthcoming solar maximum remains to
be seen.
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- Satellites are also at risk during solar
storms. The US Department of Defense has estimated that disruptions to
government satellites from space weather cost about $100 million a year,
and that even when the Sun is relatively placid, as it was in 1994 and
1995, about 150 malfunctions occur annually.
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- When the communications satellite Galaxy
IV failed last May, it brought down communications networks and put 45
million pagers out of action. The satellite's manufacturer, Hughes Electronics
Corporation, says an on-board processor failed as a result of a random
event. Others believe a more likely culprit is the Sun.
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- Killer electrons
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- Dan Baker, director of the Laboratory
for Atmospheric and Space Physics at the University of Colorado in Boulder,
and his colleagues have studied the solar weather conditions that existed
at the time of the failure. They found that a large number of high-energy
electrons had become trapped in the Earth's magnetosphere in the two-week
period before the satellite failed, as a result of exceptionally stormy
solar weather. According to Baker, it was "one of the most intense
periods that we've seen for the last two or three years".
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- Electrons with kinetic energies greater
than a million electronvolts have been dubbed "killer electrons".
They smash through the skin of spacecraft and lodge inside dielectric materials
such as thermal blankets, electronic boards, coaxial cables and electrical
insulation. If more electrons arrive than can leak away, the buildup of
charge can create strong electric fields inside the spacecraft, a process
called deep dielectric charging. Eventally, arcing occurs as electrons
jump between areas at different potentials. It is these tiny bolts of lightning
that destroy spacecrafts' electronics. "We don't know for sure if
this caused the Galaxy IV failure," says Baker, but he says several
other spacecraft also had problems during the same period.
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- And nobody knows whether networks that
have been designed in the 10 years since the last solar maximum will cope.
"As technologies change, new vulnerabilities to solar events crop
up," says Lou Lanzerotti, a geophysicist at Bell Labs, the R&D
arm of Lucent Technologies. He points to the huge proliferation of wireless
networks. "We find that there are a few solar radio bursts every solar
maximum that are larger in amplitude at Earth than the noise level in a
cellular system."
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- Could these bursts drown wireless networks
in a sea of noise, putting millions of cellphones and other wireless devices
around the world out of action? "It's something that we haven't thought
about before because we didn't have the technology and didn't need to think
about it," says Lanzerotti. With the solar maximum approaching, time
is fast running out.
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- David Appell is a science journalist
based in Gilford, New Hampshire
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- http://www.newscientist.com/ns/19990227/
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