快猫短视频

BATTEN down the hatches, there鈥檚 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.

Should one of those plasma storms hit Earth, the impact could be devastating.
Each fireball鈥攌nown as a coronal mass ejection鈥攊s a giant maelstrom
of ionised gases at temperatures of well over a million degrees. But the
temperature is the least of Earth鈥檚 worries. The plasma will tear through the
Earth鈥檚 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.

快猫短视频s 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.

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 鈭�15 掳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.

Later in the day, when public officials called for an explanation, engineers
at Hydro-Quebec, the region鈥檚 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.

Rapidly changing magnetic fields generate currents in any conductors within
reach. This is how a dynamo works鈥� 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鈥檚
transmission lines stretch for over 1000 kilometres. Power lines, telephone
lines and even railway lines are all potential conduits for 鈥済eomagnetically
induced currents鈥� (GICs) of hundreds of amperes.

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.

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.

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.

Exactly this happened to Hydro-Quebec鈥檚 power system that fateful
morning. 鈥淰oltage 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,鈥� says John Kappenman, an expert in the effects of
geomagnetic storms at the Metatech Corporation, based in Goleta, California.

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.

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 Figure).

Cycle 23 鈥渨ill be one of the largest on record, and comparable to the last
two solar cycles鈥�, says a panel of international experts chaired by Jo Ann
Joselyn of the US National Oceanic and Atmospheric Administration鈥檚 Space
Environment Center in Boulder, Colorado. They warn that the sunspot number could
reach 190, peaking sometime between June this year and January 2001.

Can anything be done to avert disaster? Leonard Bolduc, a researcher at
Hydro-Quebec鈥檚 Institute of Research in Electricity of Quebec, who was working
on the night of the failure, has studied the network鈥檚 breakdown. There is
little that Hydro-Quebec can do to prevent GICs. Instead, Bolduc says the
company鈥檚 strategy is to design grids that can cope. 鈥淗ydro-Quebec has spent a
lot of money trying to understand the phenomena and to evaluate all its
equipment during a GIC storm,鈥� he says.

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. 鈥淲e are confident that our network could now support such a big
storm,鈥� says Bolduc.

Currents and electrojets

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鈥檛 easy. The
interaction between the Earth鈥檚 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鈥檚 magnetic
field, and the way this generates currents in ionised regions of the Earth鈥檚
upper atmosphere. These currents鈥攃alled the auroral electrojet鈥攈ave
an electric field associated with them. The horizontal component of this field
at the Earth鈥檚 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.

By combining their models of the auroral electrojet and the conductivity of
the Earth鈥檚 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.

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.

Kappenman also has ambitious plans. He is division manager for Metatech鈥檚
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鈥攖he company that operates Britain鈥檚 power
transmission network鈥攚hich is installing his system this month.

PowerCast uses a model of the interaction between solar plasma, the
magnetosphere and the geology of the Earth鈥檚 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.

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鈥檚 warning of an impending solar storm.

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鈥檚 a difficult job, says Kappenman. 鈥淧ower companies
are not like phone companies where, if it gets too busy, they can give you a
busy signal. 鈥淢etatech claims that the system works with 鈥渞easonable accuracy鈥�.
Just how it it will perform during the forthcoming solar maximum remains to be
seen.

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.

When the communications satellite Galaxy IV failed last May, it brought down
communications networks and put 45 million pagers out of action. The satellite鈥檚
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.

Killer electrons

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鈥檚
magnetosphere in the two-week period before the satellite failed, as a result of
exceptionally stormy solar weather. According to Baker, it was 鈥渙ne of the most
intense periods that we鈥檝e seen for the last two or three years鈥�.

Electrons with kinetic energies greater than a million electronvolts have
been dubbed 鈥渒iller electrons鈥�. 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鈥� electronics. 鈥淲e don鈥檛 know for sure if
this caused the Galaxy IV failure,鈥� says Baker, but he says several other
spacecraft also had problems during the same period.

And nobody knows whether networks that have been designed in the 10 years
since the last solar maximum will cope. 鈥淎s technologies change, new
vulnerabilities to solar events crop up,鈥� says Lou Lanzerotti, a geophysicist at
Bell Labs, the R&D arm of Lucent Technologies. He points to the huge
proliferation of wireless networks. 鈥淲e 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.鈥�

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? 鈥淚t鈥檚 something that we haven鈥檛 thought about before because we didn鈥檛
have the technology and didn鈥檛 need to think about it,鈥� says Lanzerotti. With
the solar maximum approaching, time is fast running out.