Dr. Paul Krehbiel

SOCORRO, N.M., May 23, 2000 -- New Mexico Tech presented its Distinguished Research Award for 2000 to Dr. Paul Krehbiel, professor of physics, in recognition of his outstanding record of research in thunderstorm electrification, lightning discharges, and radar meteorology over the past 30 years. The award was presented at commencement ceremonies at the state-supported research university on May 13, 2000.

"I came to New Mexico Tech in 1966 to work with Dr. Marx Brook," Krehbiel recalls. Brook was the director of Tech's Langmuir Laboratory for Atmospheric Research. Krehbiel had earned his bachelor's and master's degrees in electrical engineering from Massachusetts Institute of Technology, and he applied his skills to developing instruments to probe problems related to thunderstorms and atmospheric electrification. Brook and fellow researchers C. B. Moore and Charles Holmes were trying to learn more about lightning and to answer questions about how thunderstorms become electrified. Krehbiel worked with Brook on developing a radar technique -- dual-polarization radar -- for studying the interiors of clouds.

Krehbiel recalled that the first major field program he was involved in was conducted on the plains northeast of Magdalena, from 1968 through 1970. "Life ever since has been one summer field program after another," he adds. "That's the best time for studying thunderstorms."

Paul's early studies of lightning charge locations inside storms, and his subsequent development of a lightning-channel-locating radio interferometer made it possible to see what lightning looks like inside thunderclouds and greatly contributed to our understanding of how lightning discharges develop and where electric charge is located in storms.

During the summers of 1976, 1977, and 1978, Paul, Marx Brook, and a group of Tech undergraduate students conducted studies at Kennedy Space Center (KSC) as part of their Thunderstorm Research International Program (TRIP). "We operated a network of twelve stations at KSC, to locate where the lightning discharges were getting their electric charge from," Paul says "There was also a network of three Doppler radars, and we operated our fast-scanning noise radar during TRIP as well." The noise radar, developed with Marx Brook, permitted much greater time resolution of processes within the precipitation-forming regions of clouds.

"My wife Kay and our children were along each summer in Florida," Paul recalls. "We stayed in Cocoa Beach. Although they didn't see much of me those summers, we had very interesting times driving cross-country each year -- without air conditioning -- and the kids learned how to swim quite well while we were there."

In 1978, Paul enrolled in the Ph.D. program at the University of Manchester Institute of Science and Technology. For his doctoral research, he analyzed the data he had gathered in the TRIP programs. As part of his Ph.D. dissertation, Paul analyzed the behavior of positive ground flashes in the decaying phase of a storm at Kennedy Space Center. Scientists now recognize that these kinds of discharges causes sprites in the mesosphere.

In a widely-cited 1979 paper, Paul and his colleagues provided convincing evidence that the main negative charge lay in the ice region of thunderclouds and was horizontally distributed throughout the ice region. This was the result of methods Paul developed for getting better time resolution of the electrostatic structure of a lightning flash.

In 1982, Krehbiel returned to Tech, where, in addition to continuing his research, he began teaching. He soon became a member of the Physics Department faculty. One of Paul's chief academic achievements at Tech was to help establish Tech's Electrical Engineering department and serve as its first chair. The program has since grown to become the largest engineering program at Tech.

Recently, Paul and his Tech colleagues Bill Rison and Ron Thomas have developed a new lightning location system, the Lightning Mapping Array, or LMA. This instrument (inspired by the Lightning Detection and Ranging system at KSC), consisting of a network of 7 to 10 or more stations over a county-wide area, has made it possible to obtain detailed, three-dimensional pictures of lightning inside storms. The system was first used to observe intense lightning activity in severe thunderstorms of the Great Plains. The results, obtained in Oklahoma, were described in a cover article in EOS, the Transactions of the American Geophysical Union, in January 2000. The Oklahoma study produced some surprising results and showed that lightning may be a valuable diagnostic tool for predicting regions of large hail and tornado formation.

Both NASA and the National Severe Storms Laboratory in Oklahoma have found the lightning mapping data so interesting that each are ordering one of the Lightning Mapping Arrays, which are being built at Tech. Meanwhile, Paul and his colleagues and students have been busily preparing for a large, two-month field study of lightning in large hailstorms along the Kansas-Colorado border. This program is called the Severe Thunderstorm Electrification and Precipitation Study, or STEPS.

Krehbiel says, "We're setting up a 15-station lightning mapping array in STEPS. Other scientists will be operating special, dual-polarization Doppler radars to understand their structure, and will fly instrumented aircraft and balloons through the storms. We'll be in a farming and ranching area that gets very large hail-producing storms, so we should be able to obtain good observations of supercell storms that produce damaging hail. We will also be studying a special type of storm in which the lightning lowers positive charge to ground instead of the usual negative charge. We're trying to find out why these positive ground strokes occur. Is the electrification of the storms inverted in polarity? This is important to understanding how storms become electrified."

Another objective of STEPS is to study horizontally extensive lightning discharges, called "spider" lightning, that occur in the dissipating stages of a storm. Positive cloud-to-ground strokes produced by the spider lightning cause spectacular glows called "sprites" in the upper atmosphere above storms. Paul's most recent Ph.D. graduate, Mark Stanley, made a detailed study of sprites for his dissertation, and will be continuing his research in STEPS using Tech's lightning interferometer.