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Airline navigation threatened by plasma plumes
http://space.newscientist.com/article/dn12921-airline-navigation-threatened-by-plasma-plumes-.html

Airline navigation threatened by plasma plumes
11:04 15 November 2007
NewScientist.com news service
David Shiga

Mysterious plumes of plasma at the edge of the Earth's atmosphere are threatening airline navigation by throwing off GPS positioning information by up to the length of a football field. But a poor understanding of how the plumes form means that accurate forecasts of the phenomena – which would allow GPS users to plan around them – are years away.

Scientists have long understood that outbursts from the Sun called coronal mass ejections can interfere with communication between Earth-orbiting satellites and the ground.

More recently, they have learned that at least some of the disruptions are due to giant plumes of charged particles, or plasma, that form in response to the solar outbursts in the Earth's ionosphere, a region filled with ions at the boundary between Earth's atmosphere and outer space. The concentrated plasma in the plumes diverts and delays satellite communications, such as GPS signals.

But forecasting these disruptions is difficult because scientists do not know exactly how the plumes form or where the extra plasma they contain comes from.

Real-time maps
There are hints that the ionosphere above the equator could be the source of the plume plasma, feeding it outward to other parts of the ionosphere where the plumes are generated. But it has been difficult to track ionosphere activity at the equator because of a lack of sensors there.

Now, scientists are trying to organise the creation of a network of GPS receivers around the equator in Africa that will calculate the distortion that the ionosphere causes to signals sent by GPS satellites. In this way they hope study the plumes and hunt for their source.

The researchers are discussing the project this week at the Africa Space Weather Workshop in Addis Ababa, Ethiopia.

"North America has thousands of GPS receivers in a network we use to monitor North American plumes," says Tim Fuller-Rowell of the University of Colorado in Boulder, US, who helped organise the meeting in Ethiopia. The data from the receivers is used to produce online maps of the ionosphere, updated every 15 minutes.

Africa has only a few dozen dedicated receivers, Fuller-Rowell says, but that may soon change. "Within a few years we hope to deploy hundreds of receivers," he says. "Five years from now we hope to be making real-time maps of the ionosphere over Africa, too."

Satellite imaging
In addition to disrupting satellite transmissions, the plumes can disrupt airline navigation and radio communications, Fuller-Rowell says.

Anthony Manucci of NASA's Jet Propulsion Laboratory in Pasadena, California, US, says measurements of the ionosphere above the equator could be important in understanding how the plumes are created.

In addition to the African GPS network, scientists would like to send up a satellite to monitor the plumes from above. An ultraviolet camera on such a satellite could provide better images of the plumes than those produced from GPS measurements, Manucci says.

"If we could go up to space and put an imager looking down, we could see these plumes form and have a much better picture of why they formed in the first place," he says.

Interesting.