Colorful displays of northern lights are a spectacular backdrop to human activity as oil pipelines and electric power systems expand into the Arctic. But is the aurora merely an uninvolved bystander?
Geophysicist S.-I. Akasofu and J.D. Aspnes of the University of Alaska say it probably is not. They report what they believe to be ''the first confirmation that auroral activity induces surges in the protective relay system of a power transmission line.'' This raises the question of whether or not the electromagnetic effects of a strong aurora could blow out an Arctic power-line system.
The aurora is an intermittent electrical discharge in the outer atmosphere. Earth's magnetic field traps electrically charged particles coming from the sun. These trapped particles bounce back and forth between the north and south magnetic poles. There is also an electric current concentrated along the auroral zone--a zone 20 to 25 degrees of latitude around a magnetic pole. This is the auroral electrojet.
When trapped particles penetrate more deeply into the upper atmosphere, they energize air molecules which then emit the light that makes the auroral displays. However, it is the electrojet current rather than the auroral light itself with which Akasofu and Aspnes are concerned.
As they explain in reporting their findings in Nature, this current, high in the atmosphere, can induce significant voltage differences along the ground. And these, in turn, can induce substantial electric currents in long conductors, such as power lines, that are grounded at widely separated points. Indeed, Akasofu and Aspnes have found power-line fluctuations of 138,000 volts and 100 amperes of current near Fairbanks, which were due mostly to auroral activity.
Now they have looked into electrical surges in the relay system that protects the Healy-Fairbanks power line. Specifically, they studied the protective system at the transformer station where the line terminates at the Gold Hill substation outside Fairbanks.
Again, they have found a significant series of electrical surges that seem to be clearly associated with auroral activity. This shows up not only in voltage and current measurements but also in recordings of the sound which the transformer makes - the so-called transformer hum. In reporting this, Akasofu and Aspnes note that some of the auroral-induced surge activity is of a kind that could possibly overheat and damage the transformer.
Whether or not this will be a serious danger to Arctic power lines or just a nuisance remains to be seen. But it does show that, as modern technological civilization moves into new environments, it can be involved in unsuspected interactions with those environments.
Over the past decade geophysicists such as Robert Helliwell at Stanford University have found that energy radiated by power lines penetrates the auroral region and interacts with the particles trapped there. Now, it seems, the aurora is striking back.