"The ionosphere, the partially ionized upper atmosphere ranging from about 37 to 200 miles above the Earth's surface, can profoundly effect radio, television and telephone transmissions signals and devices," says Dr. John D. Mathews, professor of electrical engineering and director of Penn State's Communications and Space Sciences Laboratory. "What hasn't been considered is that the ionosphere has local weather that can rapidly change. This weather includes a newly observed phenomenon we've named ion rain."
Ionization in the atmosphere is caused by ultraviolet radiation from the sun. Solar flares and other solar events influence the amounts of ionizing radiation and energetic particles that reach the upper atmosphere.
"Solar flares have caused major problems in the past," says Mathews. "During the Great Magnetic Storm of March 1989 -- which resulted from a large solar flare -- part of the power grid went down in North America. Radio and broadcast television was disrupted, as was short-wave communications. The aurora borealis was seen as far south as Florida."
While these events were occurring on Earth, the mechanism for forming layers in the ionosphere was disrupted. In essence, for a short period of time, the ionosphere was blown away from the Earth and then returned.
With an increase in reliance on satellite information for geographic positioning systems, mobile telephones and other forms of communication, changes in the ionospheric weather could influence many Earthly pursuits. Today, most ocean- going ships and most aircraft use information from geographic information satellites to navigate. The low Earth orbit satellites planned for Motorola's and other mobile telephone service will be effected by ionospheric weather.
"Recently, high resolution observation of the ionosphere using the 430 megahertz Incoherent Scatter Radar at the Arecibo Observatory, has shown the layers and associated processes of the ionosphere in unprecedented detail," Mathews told attendees at the North American meeting of the International Union of Radio Science. "These observations revealed streaks of ionization that descend through the ionosphere."
Only the 1000-foot dish at the Arecibo Observatory in Puerto Rico can make these high-resolution observations. The observatory is operated by Cornell University for the National Science Foundation. Mathews and David W. Machuga, graduate student in electrical engineering, worked with Dr. Qihou Zhou and Dr. Mike Sulzer, both of Arecibo Observatory and both graduates of Penn State, to observe images of the ionosphere that could be compared to mathematical models of what is happening in the upper atmosphere.
With the higher resolution now available, the researchers can see the intricate patterns of ionospheric weather. In the lower ionosphere, the researchers see layers of ionized metals like sodium, calcium and iron that are the remains of meteorites that burn up in this region. The metals are ionized by the ultra-violet radiation and are visible as distinct, long-lived layers when observed by the Arecibo telescope.
Higher up in the ionosphere, oxygen, nitrogen and nitrous oxide form much shorter lived ions that don't form layers but blobs and waves of ionization and "ion rain." The researchers do not expect to be able to predict fronts or weather patterns the way meteorologists do, but they would like to better understand the electrodynamics of the ionosphere.
"Ion rain, for example, is a small-scale weather process that seems to flow downward creating a streakiness in the ionospheric picture," says Mathews. "We think it looks like sheets of ionization that form in relation to the Earth's magnetic fields."
EDITORS: Dr. Mathews may be reached at 814-865-2354 or JDMathews@psu.edu by email.