With the ubiquitous Global Positioning System (GPS), scientists have gained unexpected insight into Earth's ionosphere, an electrically charged region of space that hovers over the planet. Among other uses, GPS receivers are routinely cataloging the population of electrons swirling around the ionosphere. This has led to the discovery of some odd structures in the ionosphere, including gigantic plumes of ionized gas rising steeply into space. The studies are more than idle curiosity. The plumes and other phenomena in the ionosphere can affect radio signals that pass through the region. Of particular concern are the GPS signals themselves, which traverse the ionosphere from a network of orbiting satellites to reach receivers on aircraft or the ground. Free electrons in the ionosphere twist the radio signals, changing their speed and direction of travel. Among other consequences, this could be disastrous for commercial and military aircraft operations that depend on GPS information, “The FAA [U.S. Federal Aviation Administration] is very concerned that some of these steep gradients due to these plumes could affect positioning of aircraft as they are coming in to land,” said Timothy Fuller-Rowell, a senior researcher with the NOAA Space Weather Prediction Center in Boulder, Colo. Many scientists, on a quest to learn more about disturbances in the ionosphere, are hopeful some answers may be found over Africa. Specifically, they are curious to learn how Earth's geomagnetic equator, which tracks across Africa, affects the plumes and even if they exist there at all. “It's widely understood that Africa is key to the puzzle,” said Madhulika Guhathakurta, a lead scientist with NASA's Living With a Star program in Washington, D. C. Further, as the largest landmass beneath the geomagnetic equator, Africa serves as a natural platform to study ionospheric disturbances that affect navigation and positioning, explained Fuller-Rowell. Before the discovery of the plasma plumes, the disruption of satellite signals seemed like random events. “People knew there was a space storm that must have disrupted their system, but they had no idea why,” said Tony Mannucci, who specializes in ionospheric and atmospheric remote sensing at NASA Jet Propulsion Laboratory in Pasadena, Calif. Through careful study, scientists have determined that disturbances in the ionosphere begin with storms on the Sun, which send off giant clouds of plasma that travel through space. If directed toward Earth, turbulent shock waves of charged gas and their accompanying magnetic fields hit the magnetosphere, which in turn strike the ionosphere, creating plumes of plasma. “Now we know it's not just chaos. There is cause and effect. We are beginning to put together the full picture, which will ultimately let us predict space storms,” Mannucci said. Regional networks of GPS receivers are common in North America, providing scientists with estimates of how many electrons radio signals encounter as they travel from space to ground-based receivers. NOAA is using the information to post real-time maps of the ionosphere on the Internet. As part of a United Nations initiative to expand scientific research programs in Africa, various agencies and organizations including the U.S. Department of State and the University of California, Los Angeles are organizing new GPS networks to provide, among other data, a more complete picture of the ionosphere (see Figure 1). “Our goal is altruistic, to support space science and education in Africa, but it's interesting on the science side as well,” said Fuller-Rowell. “A lot of space weather is related to the geomagnetic equator. Things are organized around it or relative to it. The plasma field is affected by electric fields and those in turn are related to the magnetic field.” Determining how these fields interact over Africa could lend insight into fundamental theories of ionospheric dynamics, he explained. For example, instead of originating at the equator, “One theory is that the plasma which forms in these plumes is coming from more mid- and low-latitude regions,” Fuller-Rowell said. “In Africa you have quite a different geomagnetic structure [than over North America]. We don't know if you would see the plumes as much over Africa.” The effort to seed Africa with GPS receivers for the ionosphere mapping project was discussed at the African Space Weather Science and Education Workshop, which met in Addis Ababa, Ethiopia, 12–16 November 2007. “Five years from now we hope to be making real-time maps of the ionosphere over Africa too,” said Fuller-Rowell. For more details, visit http://kuiper.colorado.edu/IHY-Africa/. Irene Klotz is a freelance writer for the American Geophysical Union.
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