UMass prof seeking sprites
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
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
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
"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."
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.