UMass prof seeking sprites

Steven Reising, assistant professor of electrical and computer engineering at the University of Massachusetts, has done research on sprites, a lightning phenomenon, and wants to have a station in the Amherst area to study the science of them. KEVIN GUTTING photo

By KAY J. MORAN, Staff Writer
 
 

Thursday, May13, 1999 -- (AMHERST) - During one in perhaps every 200 lightning strikes, a red glow shoots 55 miles into the atmosphere above the thunderstorm cloud. Discovered only in the last 10 years, these "sprites" have been happening for millions of years.

"They're very large - 50 kilometers by 50 kilometers by 50 kilometers," said Steven Reising, assistant professor of electrical and computer engineering at the University of Massachusetts. (Fifty kilometers equals 31 miles.) "It's really an enormous region of space."

Though sprites don't interfere with aircraft, space craft launches or satellites, scientists think they may cause chemical changes in the upper atmosphere. Much more study is needed before the full extent and effects of the phenomena are known - and some new work may take place in the Amherst area.

Today, there are only three other stations in the world that seek to monitor sprites. The creation of one in this area would be the fourth.

One station is at Stanford University in California and another is in Antarctica, funded by NASA and the National Science Foundation. The Air Force has given the researchers money to build a third receiver in Colorado.

Reising is applying for a grant to establish the fourth. He's looking for a place, he said, "as far as I can get from lights and radio waves."

Reising and collaborators at Stanford have developed a method of using radio waves to estimate the number of sprites produced by a thunderstorm without actually seeing them. He hopes soon to install a sprite-monitoring radar station somewhere in or near Amherst, if he secures a grant.

Sprites can be seen from as far as 400 miles away. But they're hard to spot.

No brighter than the aurora borealis and far briefer, a sprite is visible only to a person whose eyes are already adjusted to a dark night sky and who is looking in precisely the right spot at the exact millisecond the glow occurs.

"There've been reports by a few pilots every decade or so for most of this century," Reising said. But without other evidence, those reports were dismissed as illusions.

Commercial airliners go up to about six miles, military aircraft to 12 miles. Sprites occur in the region from 25 to 60 miles up, just below where the aurora borealis begins, Reising said.

Accidental discovery

Research on sprites began only after 1989, when aurora borealis researchers at the University of Minnesota tested a low-light-level camera by pointing it at a distant thunderstorm. To their surprise, they recorded the image of light far above the storm clouds.

Sprites have been deliberately captured on film and videotape many times since then (Images and other information on sprites are available on the Web at http://elf.gi.alaska.edu). To do that researchers need a clear line of site from their camera to the top of a thunderstorm. However, clouds or other obstructions are frequently in the way.

In the midst of his graduate studies at Stanford in the early 1990s, Reising studied the aurora borealis with a researcher at the University of Alaska at Fairbanks who told him about sprites. Reising decided to focused his doctoral dissertation research on those elusive, fleeting glows.

He worked with Umran Inan and Timothy Bell of Stanford University, and their findings were published in the April 1 issue of Geophysical Research Letters, published by the American Geophysical Union.

"It was exciting to get in on this on the ground floor," said Reising, who joined the UMass faculty in July and works in the Microwave Remote Sensing Laboratory in the Knowles engineering building. "This is something in nature that wasn't studied before."

Counting sprites

A sprite is the glow of nitrogen ionized above a thunderstorm when a strong lightning strike transfers a large amount of positive electrical charge from cloud to ground.

By comparing their measurements of radio waves due to lightning with the video evidence of sprites, Reising and his collaborators developed a way of telling from the radio waves alone how many sprites have been produced.

"One can monitor lightning all over the hemisphere using only four stations," he said. "It's relatively inexpensive," with the equipment costing about $15,000.