CMEs - If The Sun Spits,
The Earth Could Fry
By David Appell
If the Sun spits, the Earth fries. Humankind is ill-prepared for the furious climax of the next solar cycle.
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.
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.
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.
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.
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.
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.
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'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.
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 <
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.
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.
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.
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'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.
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.
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'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.
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.
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.
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.
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'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.
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'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".
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.
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."
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.
David Appell is a science journalist based in Gilford, New Hampshire