U. scientist tracks world's worst storms

The world's most ferocious thunderstorms have been tracked to their lairs by a team of scientists including the University of Utah's Edward J. Zipser.

Some of the worst are, as expected, in the Midwestern United States. But others are a bit of surprise.

The research is reported in the August issue of the Bulletin of the American Meteorological Society, available online; the bulletin's home page is www.ametsoc.org.

"Where Are the Most Intense Thunderstorms on Earth?" lists as lead author Zipser, professor of meteorology, and as co-authors the U.'s Chuntao Liu; David P. Yorty, North American Weather Consultants, Sandy; Daniel J. Cecil, University of Alabama, Huntsville, Ala.; and Stephen W. Nesbitt of Colorado State University, Fort Collins, Colo.

"This is basically the culmination of something like eight years of the Tropical Rainfall Measuring Mission satellite," Zipser said in a telephone interview. The weather satellite, which goes by the acronym TRMM, was launched in 1997 and is a joint venture of NASA and the Japan Aerospace Exploration Agency.

TRMM has the only radar in orbit that can measure precipitation. In addition to the radar, it carries instruments to detect water ice in the atmosphere and lightning strikes. It checks these factors between 35 degrees north latitude and 35 degrees south.

"Measuring rain from space is an extremely important objective," Zipser said. The space radar provided a set of tools, as did other instruments carried by TRMM. Suddenly, he and other members of the satellite's science team "were like kids in a candy store, when we started using the data."

Members of the group realized that one of the studies they could carry out that was never done before was to examine the intensity of thunderstorms around the world.

The satellite's passive microwave imager, visible and infrared scanner and lightning sensor provided important indications of storm intensity.

"Most storms have ice particles, snow or hail in them, if they go high enough," Zipser said. Thunderstorms are usually composed more of ice than water, he said. "Lightning, in fact, requires ice particles for a charge separation."

The satellite's charge sensor shows the lightning flash rate of thunderstorms. "Some of these storms may flash several hundred times a minute."

Lightning flash rate, amount of ice water and the radar reflections help scientists to calculate a storm's intensity.