Future space-based lightning detection and reporting of lightning flashes in real-time will provide valuable additional information to existing weather sensing systems. This capability will give weather forecasters the ability to more readily evaluate threats due to lightning, thunderstorm intensity and growth, as well as storm dissipation throughout the United States.
These are the conclusions of research conducted by scientists from NASA's Marshall Space Flight Center and the Global Hydrology and Climate Center in Huntsville, Alabama, in conjunction with researchers at the Massachusetts Institute of Technology (MIT), NASA's Kennedy Space Center, the National Weather Service (NWS) Office in Melbourne, Florida, and operational meteorologists with the U.S. Air Force's (USAF) 45th Weather Squadron at Cape Canaveral Air Station. The results will be presented today at the American Meteorological Society Seventh Conference on Aviation, Range, and Aerospace Meteorology in Long Beach, California.
In the summer of 1996, scientists began a study to determine how continuous, real-time lightning detection from space might provide added knowledge to the weather forecaster in the identification and warning of thunderstorm hazards.
"Past studies have repeatedly indicated the strong correlation between electrification and the dynamics of thunderstorms," said Dr. Steven Goodman of the NASA/Marshall Space Flight Center, and principal investigator of the experiment. "What we have done here is develop these concepts into real-time algorithms." The scientists developed an interactive display environment that promotes the use of total lightning measurements, in addition to conventional radar data, as an indicator in identifying severe storms and storm morphology.
The Melbourne (Florida) Weather Service Office was selected as a testbed to conduct this study because of the unique availability of real-time lightning and radar data. It serves as an experimental forecast office for the NWS, and as an Applied Meteorology Unit for NASA, USAF, and NWS.
The enhancements to lightning detection and forecasting capabilities could also improve space launch weather support at USAF/Cape Canaveral Air Station and NASA/Kennedy Space Center. Natural triggered lightning hazards are a significant threat to space launch. Approximately one-third of the launches are delayed or scrubbed due to adverse weather. According to Mr. William Roeder, 45th Weather Squadron's Chief, operations Support Flight, the launch weather teams would benefit from improved lightning sensing and warning.
An additional element of the experiment involves the use of space-based observations of both in-cloud and ground discharges from NASA's Optical Transient Detector (OTD). The OTD data are available 12-24 hours following collection for retrospective analysis and validation studies. The OTD, launched in April 1995 as a scientific payload aboard the MicroLab-1 satellite, is in a low-earth orbit, and provides an early demonstration of the technology to map lightning from space at storm-scale resolution both day and night. The satellite is at an orbital altitude of approximately 750 km (about 470 miles), which provides a total field of view of 1300 x 1300 km (813 x 813 miles).
The results presented in the study demonstrate in several ways the incremental value of observing the total lightning in-cloud and the discharges to ground in diagnosing the structure and characteristics of thunderstorms:
- Dr. Ravi Raghavan, of the Universities Space Research Association and experiment co-investigator, says the high temporal resolution of the LDAR data provides a rapid update on the evolving storm cells that enables scientists to continually characterize the structure, morphology, and hazards of active storm cells.
- Based on responses obtained from forecasters, the total lightning measurements
provided by the LDAR were extremely valuable for identifying the existence,
intensity, growth, and dissipation of thunderstorms. This capability is
very useful during the "heat of battle", when numerous, potentially
hazardous storms are simultaneously growing and decaying in the forecast
warning area of responsibility.
It is noteworthy that the total lightning measurements were very useful in identifying storm dissipation from the view of inclusion or exclusion of thunder in aviation terminal forecasts (and eventually Transcribed Weather Broadcasts). "This is especially critical in the modernized weather service as the temporal accuracy of forecasts is being improved," said Dave Sharp, Science and Operations Officer at the Melbourne Weather Office. There are cases where the cloud is electrically active even after the final discharge to ground occurs.
Total lightning information adds considerable confidence to the safety margin forecasters include in their aviation products.
- Total lightning measurements with high temporal resolution can also
be used to specifically address the risk of injury from lightning strokes.
It has been found that the LDAR flashes typically precede the initial cloud-to-ground
discharges by about 4 minutes. Thus, it may be possible to use this lead
time in issuing lightning watches/warnings, according to co-investigator
Dr. Earle Williams of MIT.
In a related study conducted by the NWS office at Melbourne, LDAR system was used to assist forecasters of the lightning threat in the vicinity of the Olympic soccer tournaments, which were held in the Orlando, Florida area during the summer of 1996.
NASA is demonstrating that real-time lightning detection from space during day and night with the resolution to resolve individual thunderstorm cells is now possible. "The most capable space sensor developed for lightning detection is the OTD, but we don't yet have continuous observations of the continental United States in real-time," said Goodman. "Therefore, we utilized the local ground-based lightning detection capability to demonstrate the value-added by having real-time detection throughout the thunderstorm life-cycle."
Forthcoming sensors such as the Lightning Imaging Sensor (LIS), scheduled for launch in late 1997 aboard NASA's Tropical Rain Measuring Mission (TRMM-1) observatory, will continue to demonstrate the additional diagnostic storm information provided by observing the lightning produced by thunderstorms. In the future, however, lightning sensors will be placed in geostationary orbit, perhaps on the next generation of operational weather satellites. These sensors will provide lightning data that are available both day and night, and at the forecaster's workstation within 30 seconds of occurrence. From their position in geostationary orbit, these sensors will be able to survey all of the United States and nearby oceans, rather than just one limited geographic area. A constellation of lightning sensors could someday provide global coverage of the major continents and oceans.