Tuesday, March 4, 2008

The Mystical Aurora Borealis

My earliest recollection of the Aurora Borealis, the Northern Lights, is from a song of the 1950s called "the Northern Lights of Old Aberdeen", which I always took to be a reference not to Scottish traffic arrangements but to the celestial phenomenon of bands, curtains or streamers of coloured light that appear in the sky predominantly in the Arctic and Antarctic regions of the earth. In the Antarctic, the lights are called the Aurora Australis, or Southern Lights. They are visible, though less frequently, also outside those zones. I do not know how often the Northern Lights appear in northern Scotland but in the far north of this country, in Finnish Lapland, the number of auroral displays can be as high as 200 a year. In southern Finland the number is usually fewer than 20.

Folklore abounds with explanations of the origins of the spellbinding celestial lights. In Finnish they are called "revontulet", which means "fox fires" a name derived from an ancient fable of the arctic fox starting fires fire or spraying up snow with its brush-like tail. No matter that in English "foxfire" is a luminescent glow emitted by certain types of fungi growing on rotten wood. The true story is that the sun is the father of the auroras.

The sun gives off high-energy charged particles (also called ions) that travel out into space at speeds of 300 to 1200 kilometres per second. A cloud of such particles is called a plasma. The stream of plasma coming from the sun is known as the solar wind. As the solar wind interacts with the edge of the earth's magnetic field, some of the particles are trapped by it and they follow the lines of magnetic force down into the ionosphere, the section of the earth's atmosphere that extends from about 60 to 600 kilometres above the earth's surface. When the particles collide with the gases in the ionosphere they start to glow, producing the spectacle that we know as the auroras, northern and southern. The array of colours consists of red, green, blue and violet.

The Northern Lights are constantly in motion because of the changing interaction between the solar wind and the earth's magnetic field. The solar wind commonly generates up to 1000,000 megawatts of electricity in an auroral display and this can cause interference with power lines, radio and television broadcasts and satellite communications. By studying the auroras, scientists can learn more about the solar wind, how it affects the earth's atmosphere and how the energy of the auroras might be exploited for useful purposes.

An important centre for this type of geophysical study is located in Sodankylä, a small community in the heart of Finnish Lapland, at latitude 67.4 degrees north. It is an excellent location for probing the secrets of the earth's geomagnetic field. It was here that the Finnish Academy of Science and Letters established a geophysical observatory in 1913. Today, the Sodankylä Geophysical Observatory (SGO) is run by the University of Oulu. In addition to research the observatory performs routine geophysical measurements at its different stations. They produce ionospheric, geomagnetic and auroral data as well as seismic, cosmic ray data from Finland.

The observatory and its associated research units nearby form a scientific community devoted to work that has global significance. There are high hopes that the brainwork of the scientists will also have beneficial effects on the local economy in this part of Lapland. The idea is that the findings of scientific research can be used to attract high-tech firms to the area, generating jobs and stimulating commercial activity. Already tourists can visit the privately operated "revontulikota", an auroral observatory and planetarium built in the shape of the traditional Lapp dwelling that is known as a "kota".

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