Radar unravels the mysteries of aurora borealis

By in News

Science Writer

Just east of Saskatoon there stands a row of tall thin towers, something visually like telephone lines, observing four million square kilometres of sky.

This is one of four Super Dual Auroral Radar Network radar sights operated by the University of Saskatchewan.

SuperDARN is an international array of intersecting radars, 13 in the northern hemisphere and seven in the southern. The radars record irregularities in the electrically charged, or ionized, gas that comprises the ionosphere, a layer of the atmosphere 80 to 1,000 kilometres above the Earth.

In the upper atmosphere, as under high heat, the ionized gases actually enter a fourth state of matter: plasma. The three familiar states of solid, liquid and gas have definite properties of volume and shape — a liquid, for example, takes the shape of its container but its volume cannot be compressed.

Like a gas, plasma has no definite shape or volume, so it can be compressed. But the fourth state is extremely sensitive to magnetic fields, forming clouds, filaments and beams.

The sun’s electromagnetic field is irregular, and its interactions with the plasma ionosphere constantly alters its structure.

“The interaction of the solar wind with the Earth produces the great auroral displays that we normally see from Saskatoon,” explained University of Saskatchewan physics professor Jean-Pierre St. Maurice.

The blue, green and purple light shows of the aurora borealis are actually strong electrical currents. And while ethereal, they have a significant impact on earthly activity.

As you may have seen from your own backyard, the northern lights can go from small sheets of colour to full-sky explosions nearly instantaneously. That sort of shift is a sign of a huge change in electrical currents.

Whole power lines can be knocked out by the activity, with massive power surges and outages. GPS systems are particularly sensitive to major electric activity in the ionosphere, which interferes with satellite signals.

Any Earth-orbiting satellites can lose altitude control in the face of major electro-magnetic activity, and their instruments can be severely damaged.

The SuperDARN project records as much of this turbulence as possible. Here in Saskatoon, researchers are trying to figure out what causes those systems to change the way they do.

The radars operate in pairs, collecting data in real time over the same area. Researchers can pinpoint the motion of the structures of the plasma using Doppler shift properties. If an observer is moving closer to the source of a wave — in this case sound from the radar bouncing off the plasma — the waves will seem squished, and have a higher frequency. For an observer moving away from the source, the frequency appears lower.

The four U of S radars were developed by the U of S Institute of Space and Atmopheric Studies, under current guidance of George Sofko and St. Maurice.

St. Maurice, JP to his students, is a brilliant professor whose research interests only invigorate classroom discussion.

“I think of these systems as behaving like milk poured into hot coffee after you’ve given it a little stir. You see clouds and swirls forming complex patterns — the aurora and even the solar cycle show similar kinds of turbulent structures.”

It’s a rather tall order, and thankfully there’s an international network of people working on the puzzle. The SuperDARN network is an active and communicative one, with workshops every year and meetings to publicize research.

With information instantaneously available from any of the satellites, physical meetings spur innovation and discussion.

St. Maurice is looking for relationships between structures in the northern lights, tiny (a metre) to huge (a few hundred kilometres), along with the development of turbulence in the medium, among other questions.

“I like to look at data sets in detail, identify anomalies, make sure they are not artifacts, and then pull my imaginative powers to go after an explanation. After that there is always the math and the heavier theories that invariably follow.”

Currently, the U of S is collaborating with the University of Calgary, working on another tool to unravel the mysteries of the aurora.

The project is a new radar that will look at the noise in the plasma itself. This particular radar will be the most advanced of only 10 in the world. It will provide data on density, temperature and velocity of the plasma with extraordinary resolution. Combined with the SuperDARN network already in place, it’s an opportunity for remarkable new insight into our skies.

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