Mapping the sun's energy

(The Chief Engineer)

Engineer Allister Babington engages low gear in his tough Toyota SUV and plows across the boggy terrain towards a lone hut. Strung out across the open ground are a series of 20 towers - 16 in one row, four in another parallel row. Each tower is 50 foot high, topped with antennae silhouetted against the icy winter sky.

Next to the hut is a radar dish. Inside, an air conditioner provides cozy relief from the midwinter chill, where the temperature stays stubbornly in the low 30s. The hut is packed with high-tech gear and computers, numbers constantly recording a mass of incoming data. But there are no other people: apart from Allister, who has come to check everything is running smoothly, and to give The Chief Engineer a tour, the station is fully automated.

We are at the Unwin auroral radar site at Awarua, on the southern tip of New Zealand's South Island. Free from radio interference, it's one of best high-frequency receiving sites in the world. As early as 1902, a massive 300-foot wooden "spark" tower, for sending and receiving Morse signals, was operating here. Now just its wooden base remains, as well as some original wooden houses, imported from Germany.

The radar site is named after Dr. Robert Unwin, an internationally recognized pioneer in ionospheric physics and radar detection of the ionosphere. In 1957 he established an optical station at the Awarua Radio Site, where the current radar is located.

The Unwin radar, along with its partner radar at Bruny Island in Tasmania, is run by La Trobe University in Melbourne, Australia. The full name of the project is Tasman International Geospace Environment Radars (TIGER). TIGER in turn is part of an international network of similar high-frequency (HF) radars called SuperDARN (Super Dual Auroral Radar Network).

As proof that nations truly can work together when it comes to science, SuperDARN consists of a mini United Nations: the United States, Canada, Australia, New Zealand, Great Britain, Iceland, Norway, Sweden, Italy, Japan and South Africa.

The TIGER Unwin station is one of 18 similar stations - eleven in the northern hemisphere, and seven in the southern hemisphere. Some are based in the United States and Canada, some in Iceland and Scandinavia; in the southern hemisphere, in Australia, New Zealand, South Africa and Antarctica itself. Further ones in Siberia, northern China and Antarctica are anticipated.

All are targeting their beams towards the Polar latitudes. Together, they are measuring an area roughly equivalent to a fourth of the Earth's surface.

To get an inkling of what they are looking for, glance outside, towards the sun. At Awarua on a winter's day, only pale beams filter through occasional breaks in the overcast sky. At extreme latitudes in both the northern and southern hemispheres, winter means darkness for months on end, while summer days stay light for 24 hours. Yet, high above, some 93 million miles away, the sun is neither a pale orb nor gentle warmth on your face nor even a friendly yellow disk. It's an angry, heaving, violent nuclear furnace, a medium-sized yellow star now halfway through its life cycle. The sun's light takes just eight minutes to reach Earth. Sometimes, the sun sends out massive bursts of energy, coronal mass ejections or CMEs, electromagnetic storms some believe pack as much power as the world's entire nuclear arsenal.

Another picture you seldom see: we imagine Earth's atmosphere as the breathable stuff that extends a few miles above our heads. In fact, says TIGER team leader Professor Peter Dyson of La Trobe University, the atmosphere extends tens of thousands of miles further out, becoming more and more tenuous and primarily under the control of the Earth's magnetic field which interacts directly with the solar wind.

Solar storms can create havoc. They can disrupt telecommunications on Earth, including mobile phone systems, by causing voltage surges. They can even knock satellites out of their orbit. In 1989 a solar storm left six million people in Canada without electricity. In 2003, another solar storm caused power cuts in Sweden. It also damaged several satellites and spacecraft, including the Mars Express probe.

Solar storms, even of less severity, also increase the activity of the Northern and Southern lights - Aurora Borealis in the northern hemisphere, and Aurora Australis in the southern hemisphere. These appear as spectacular curtains of light, alternating in color from purple to green and gold, strung across the horizon. "You go wow, it's just absolutely amazing," says Allister Babington. "It spreads over a whole area of the southern sky, subtly changing.

"When there's an aurora, a burst of energy from the sun on the horizon the Earth's magnetic shield, it just becomes visible, and disturbed and changing and fluctuating."

The solar wind confines the Earth's magnetic field to a region we call the magnetosphere, explains Professor Dyson. "It has a comet-like shape with a boundary about 25,000 miles from the Earth on the dayside facing the sun and a long tail extending probably 4 million miles or more out into the nightside. Some solar wind particles enter the magnetosphere and a complex series of processes results in energetic electrons and protons speeding down along magnetic field lines and causing aurora by striking atoms and molecules in the atmosphere as low as 60 miles above the Earth, causing them to give off light. The process is the same as occurs in a TV in which electrons are fired at different phosphors on a screen to produce three primary colors and hence color TV pictures."

Normally aurora occur at relatively high latitudes, but the solar wind is "bursty", causing changes in the magnetosphere location, changes in the location of aurora, and other effects we collectively call magnetic storms.

"Large events, such as CMEs cause major magnetic storms during which the aurora changes location rapidly and appears at much lower latitudes than usual. The location of aurorae can change 300 miles in less than a minute during magnetic storms, disrupting navigation and communication systems."

Once the sun's corona ejects huge amounts of matter that reach the Earth, there are rapid changes in the wind speed and pressure. The energy that enters the magnetosphere also affects the ionosphere and signatures of these effects are detected by the TIGER radars.

John Devlin, of the Department of Electronic Engineering at La Trobe University, explains what happens. "It is in this region of the ionosphere around the poles that the Earth's magnetic field lines can be'open' and connect directly to the solar wind so that energetic particles from the solar wind can be injected directly into the Earth's upper atmosphere.

"This happens to some extent all the time, but is particularly severe during solar storms when these processes can cause auroras to occur at lower latitudes locations and be seen over most of New Zealand and much of the United States. The Unwin radar studies the phenomena associated with the radio aurora that is closely linked to the visible aurora.

"The solar wind is studied by many scientific satellites, as well as ground observations. These observations are to unravel the causes of the phenomena and are also collected and used to assess and predict space weather."

TIGER monitors such storms and provides real-time data on space weather storms. The Unwin radar reaches to the high latitude ionosphere south of New Zealand. The radar has a range of about 1,800 miles and so can detect the effects of changes in the ionosphere in the region where aurora generally occur.

Professor Peter Dyson says the two radars alone, in Tasmania and New Zealand, explore an area half the size of Australia. They explore the impact of solar disturbances on Earth by monitoring the location of aurora and related phenomena occurring in the ionosphere, 60 to 200 miles above the Earth.

"The radars direct HF radio signals via the ionosphere towards Antarctica and detect weak echoes from structures in the ionosphere. These echoes are used to form images of the ionospheric structures and measure their speed and direction of motion.

"The radars also detect echoes from meteors, which are used to calculate wind speeds at heights of around 100km. Signals scattered from the sea are also detected and methods of deducing the sea-state from these signals are being developed."

Dyson says results from the operation of TIGER and the wider SuperDARN project include greater knowledge of space physics and space weather processes. These in turn improve management of radio communications and navigation systems such as GPS. There are also benefits for satellite operations and magnetic surveying for minerals and electricity supplies. The practical spin-offs are enormous. If solar disturbances and the consequent effects on the Earth's space environment can be predicted, preemptive measures can be taken, protecting power stations, satellites and communications systems. Of course this is already being done by various national agencies around the world but improved predictions would bring immediate benefit and improvement will come from understanding in detail the physical processes involved, says Professor Dyson.

Each year all the parties involved in the SuperDARN project meet to discuss new results, operational issues, and plan future programs. This year the meeting was in Virginia and one of the major topics was the new results from the few radars, including the TIGER radars, that can study the auroral motion as it moves to lower latitudes. One of the major planning outcomes was agreement to develop operational modes for the whole SuperDARN network to undertake studies in collaboration with the up-coming THEMIS satellite mission which will use five satellites to study the aurora.

TIGER is controlled remotely from La Trobe University in Melbourne, Australia. It uses HF radio waves in the 8 to 20 MHz range.

Now here's a real contrast in power: talk of an electromagnetic storms and solar power being more powerful than the world's entire nuclear arsenal may make you think you need some pretty powerful pieces of equipment to watch what's going on. Not so! TIGERUnwin consumes only 2 kW of power, the same as some electric kettles and transmits an average of 200W - the same as two bright light bulbs.

Building the station, however, proved to be an exercise in extreme precision for Allister Babbington. His firm, ASI Limited, also maintains communications equipment for the police and installs broadband wireless receivers and transmitters. Among his latest projects is an antenna for receiving radio signals from ear tags worn by cattle - a way to speed up the sorting process for farmers.

Each of the radar towers is aligned precisely to face the Southern Ocean. They are precise in each plane, vertical and horizontal, to a tolerance of just 3mm. Galvanized steel towers were assembled in two parts. The antennae were shipped in from the U.S. Construction took nine months, in boggy conditions - but at least he didn't have to cope with permafrost or lots of snow. "Relative to building a bridge it's not a huge project."

The 16 towers in line are the main transmitting and receiving radars. The other four, 75 feet or 100 meters away, are known as the interferometer. "Their function is to receive the same signals as the front ones, but they use the time difference between the front and the rear to work out the elevation angle that the waves are coming in on, so from that they can work out the locations of the signals being returned.

"The main array, the 16 antennas, form a beam that is about 3o wide in azimuth. The beam is steerable electronically which means that the towers physically stay where they are but they time delay the transmission signal to each successive tower so that they can step the beam a total of 54 degrees in azimuth."

The beam is wide in elevation and pointed towards Antarctica. Signals scatter back from turbulence in the ionosphere providing the main information needed. Some signals bounce off the Earth's upper atmosphere and down to the ocean beyond the horizon, then come back on the same path.

All antennae are fed with a co-axial cable to get the signals to and from the building. All are phased together so that the whole array forms the desired beam.

The information is collated with computers and fed back over satellite to Australia - and further afield.

From the sun to the Earth, from a radar array to the upper atmosphere and back, then via satellite around the world - solar radiation is a show that's always on, keeping scientists and engineers on their toes, and reminding us that, for all our ingenuity, we all remain subject to the powers of the universe.

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