SCIENCE

The northern lights probed

Pat Ohlendorf February 1 1982
SCIENCE

The northern lights probed

Pat Ohlendorf February 1 1982

The northern lights probed

SCIENCE

Pat Ohlendorf

When ice sheets begin covering the Beaufort Sea and the sun no longer peeks over the horizon, most visitors to the high Arctic head for home. But not a team of 65 scientists and technicians from Canada, the United States and Scandinavia. To these specialists, winter—with its 24 hours of darkness per day—is the best possible time to study the elusive and mysterious “daytime” aurora borealis, the red northern light that dances in the arctic sky. And the barren coast near Cape Parry, one of Canada’s northernmost outposts, is the most accessible place from which to launch research rockets into a poorly understood area of the Earth’s magnetic field connected to the red aurora. After a month at Cape Parry, the scientists are now beginning to unravel and decipher miles of magnetic tape containing the data radioed back by the project’s five rockets. When the Canadian group meets for a brainstorming session later this month, the first stage in validating or disproving current theories will begin. “It’s pure science,” emphasizes Fokke Creutzberg, chief Canadian scientist of the joint effort. “But we’re getting at very fundamental knowledge: how the atmosphere retains its integrity, how we are shielded from outside influences, and how we are managing to survive on this planet.”

So far, the conflicting findings gathered from space and ground observations have given rise to differing theories about how the streams of protons

and electrons known as solar wind enter the Earth’s magnetic field. Also in question is what impact this foreign material has on the atmosphere. And although sounding rockets have pierced the daytime aurora region before, a coherent overview has not emerged.

Enter project CENTAUR (Cleft Energetics, Transport and Ultraviolet Radiation), sponsored by Canada’s National Research Council (NRC) and the U.S. National Aeronautics and Space Administration (NASA). Says Creutz-

berg: “CENTAUR is the most ambitious and best-co-ordinated attempt to make extensive measurements on many different aspects of the daytime aurora.” The Canadian contribution is about a third of the $4-million price tag.

During the past decade, other studies of the nighttime auroras and the Earth’s magnetic field have stroked in the broad outlines of the picture: emanating from the Earth’s magnetic poles are lines of magnetic force that surround the Earth like a gigantic bottle. If it were visible, this “bottle,” or magnetosphere, would appear as a teardrop up to 30 times the size of the Earth, with the rounded end always facing the sun and the tail fading off into infinity on the night side of the planet, while the dwarfed Earth spins inside it like a suspended marble.

The main benefit of the magnetosphere, as far as scientists can tell, is to shield the Earth and its atmosphere from daily buffetings by the solar wind that rips away from the sun during solar magnetic storms and barrels toward the Earth at a pace approaching the speed of light. If the magnetosphere were not present to repel and capture these particles, they would wreak havoc on the atmosphere, generating dangerous radiation and destroying the delicate ozone layer, which filters the sun’s ultraviolet light.

But as it is, the solar wind gives rise to the most striking and mystifying phenomenon in the night sky. For generations, the Inuit have imagined the dancing northern lights, or arsaniit, to be a celestial ball game and have warned their children not to play outside at night—above all, not to whistle.

Otherwise, the sky people, always on the lookout for new balls, might swoop down to chop off their heads. The current scientific theory on what causes auroras is more prosaic. The trapped electrons and protons in the solar wind, researchers believe, stream along lines of force to a vast reservoir at the rear or night portion of the magnetosphere. Here they become accelerated and energized. (The CENTAUR data should help to explain why.) As the energized solar particles interact chemically with molecules in the atmosphere, they produce cascades of grey, green, purple, or red light, the color depending on the altitude and energy of the particles.

But one main target of CENTAUR’s experiments was the reddish aurora on the opposite, or daytime, side of the Earthemdash;visible only at midday during the winter in the polar regions. This unusual aurora is red because the particles causing it have low energies and are very high (about 200 km) above the Earth. It glows near the top of the other main target of the NRC-NASA quest: an apparent “hole in the bottle,” which some scientists believe to be the main entry point for the solar wind. There are, in fact, two “holes”emdash;called cusps or cleftsemdash;in the magnetosphere, both facing the sun, one near the north, the other near the south magnetic pole.

If the solar wind does enter the magnetosphere at the cusps, then scientists will have to discern exactly what sorts of particles come in and how they enter. While scientists know that the solar particles have not merely been building up inside the magnetosphere for eons, they are unsure about how the particles are kept balanced in the Earth’s atmosphere. Perhaps some form hydrogen atoms; others may blow away. The energized particles that create the aurora, Creutzberg suggests, probably vanish out in the direction of the moon. “Ultimately they may connect with magnetic fields from the sun or from elsewhere in the galaxy.”

Intent on untangling the muddle, the CENTAUR team sent five rockets soaring through, and over, the red aurora and the top of the cusp. On board were sensitive instruments to measure magnetic and electric fields, temperature, radio waves, optical properties and the energy and mass of the particles. During their 15-minute flight, the rockets radioed data back at a rate of 200,000 numbers per second, totalling more than 164 million pieces of information per rocket per flight. This foray into pure science may also generate some practical information. Shortwave radio fans may learn why the solar wind interferes with radio transmission. In addition, some clues may emerge to explain how, if at all, solar particles influence weather patterns. lt;£gt;