For Release: Sep. 25, 1995

Steve Roy
Office of Media Services
(205) 544-0034
steve.roy@msfc.nasa.gov

RELEASE: 95-46

NASA LIGHTNING DETECTOR GATHERS CLUES TO FORMATION OF SEVERE WEATHER AND TORNADOS

NASA research scientists have taken an important step toward understanding the characteristics of lightning produced by severe, tornadic storms, using data collected by a new orbiting lightning sensor launched this spring.

As NASA's Optical Transient Detector passed over Oklahoma April 17, the instrument observed intense lightning activity from a very large tornado producing storm system. These observations are significant because lightning flash rates are believed to be an important product of severe storm development and may provide an indication on the formation of mesocyclones and tornadic activity, according to Dr. Hugh Christian, Principal Investigator of the Optical Transient Detector at the Marshall Space Flight Center in Huntsville, Ala.

About 40 seconds into its pass over the Oklahoma storm, the instrument recorded a peak rate of sixty flashes per second. The rate then began to decrease. Approximately one minute after the pass, observers saw a tornado touch the ground. The instrument detected almost 200 lightning flashes during its three-minute pass. In contrast, the ground based National Lightning Network, which detects only cloud to ground flashes, located nine flashes during the same three-minute period. This large difference suggests the tornadic storm was producing primarily intracloud lightning.

"These observations of intracloud lightning activity in the Oklahoma storm system are an important indication of the potential role lightning may play as an indicator of severe weather," said Christian. "We saw much more intense lightning activity produced by these clouds than was observed on the ground, both prior to and during tornado formation," explained Christian. "In the next months we plan to perform detailed studies on the relationship between intracloud lightning and the formation of severe weather."

Previous research suggests that high ratios of intracloud and cloud-to-ground lightning are characteristic of very intense or severe thunderstorms. Observations of lightning behavior associated with severe storms show that lightning rates increase as the storm grows, but abruptly decrease as the storm begins to collapse. This pattern observed in the Oklahoma storm may mirror the life cycle of the airmass of storms and might be an indication of the onset of downdrafts occurring prior to tornado generation, according to Christian.

"The Optical Transient Detector is working wonderfully; detecting and locating intracloud and cloud to ground lightning all over the globe, during both day and night," said Christian. "The instrument has detected a great deal of lighting especially while passing over large storm systems. While the ground networks only see a portion of the total lightning activity, from space we are able to detect large amounts of intracloud lightning, as well as lightning to the ground."

"The Optical Transient Detector research effort is off to an exciting start," explained Christian. "We are increasing our understanding of the role of lightning in the Earth's atmosphere and building a data base of lightning activity as an indicator of strong convection and severe weather. The experience we are gaining with this lightning instrument could help develop geostationary sensors for real-time severe weather warnings."

Data from the Optical Transient Detector will be analyzed by scientists located at the Global Hydrology and Climate Center in Huntsville. Data will be processed in the climate center's Optical Transient Detector Science Computer Facility and archived and distributed in the Earth Observing Systems Data Information System.

The Optical Transient Detector was carried into orbit aboard a Pegasus launch vehicle provided by Orbital Sciences Corporation April 3. The instrument, managed by the Marshall Center, is a highly compact lightning detector capable of observing instantaneous changes in light intensity in its field of view, day or night.