The Aurora Makes Waves on the Ground, Too
On July 13 of this year, the earth experienced a massive bombardment of electrically-charged particles (primarily electrons and protons) which had been ejected from the sun a few days earlier during a major solar disturbance.
These periodic outbursts, so annoying to CBers and other shortwave radio operators because of the interference which they create with transmissions, have their beneficial side effects to students and admirers of the aurora. In reality, although a major aurora was produced by the bombardment on July 13, the skies were not dark enough in Alaska for the display to be visually observed.
The spectacle was not overlooked, however, by scientists at the Geophysical Institute or the Electrical Engineering Department at the University of Alaska, or by engineers of the Golden Valley Electric Association on (GVEA).
As industrial growth extends toward higher and higher latitudes, more is constantly being learned about unexpected effects that the aurora can have on routine human activities. Among the most significant of these is the setting up of voltage surges in long-distance power or telephone lines, or any conducting medium such as the oil pipeline (or in the earth, itself, for that matter).
During an intense auroral display, an electrical current of up to several million megawatts is discharged in the ionosphere at altitudes of about 60 miles (100 km). For comparison, the entire Susitna hydroelectric project would produce only about a couple thousand megawatts. The enormous electromagnetic fields produced by an active aurora induce voltage differences on the ground beneath. The difference can be as much as 10 volts per kilometer (0.6 miles) and is cumulative. That is, the farther the spacing between two grounded points, the larger the difference. As a result, electric currents flow along any conductor which connects two points on the ground under an aurora.
Power transmission lines are one facility most directly impacted by these disturbances, and the effects are monitored continuously by the Geophysical Institute and the staff of GVEA.
During the magnetic storm of July 13, a number of instruments operated at the Geophysical Institute and by GVEA at the Gold Hill substation west of Fairbanks recorded the current induced in the power transmission line between Fairbanks and Healy. As the storm intensified, current surges in the power line fluctuated as much as 10 amperes, while the "earth currents" in the ground below behaved in a similar manner.
While no power outages were experienced during this episode, blackouts or irregularities in power supply during intense geomagnetic disturbances have occurred repeatedly in the past, most notably in Canada.
Circuit breakers connected to a monitoring "relay current," such as the one at the Gold Hill substation, protect the power transmission system and the consumer from overloads.
From a longer-range point of view, auroral scientists are now working with solar physicists to provide reliable forecasts of geomagnetic disturbances to power companies and communication facilities, as well as to the defense systems.
