|
NEW
METHOD STRIKES AN IMPROVEMENT IN LIGHTNING PREDICTIONS
 |
|
 |
| Image
1 | | | A
new lightning index that combines measurements of water vapor in storm clouds
with data from Global Positioning Systems has improved lead-time for first lightning
strikes from thunderstorms. The index will help greatly aid NASA Space Shuttle
launches at Kennedy Space Center, Fla, and other commercial and DOD launches from
Cape Canaveral Air Force Station, Fla.
“Better forecasting and more advance warning of lightning strikes will help
reduce the delays or cancellations of shuttle launches from Kennedy Space Center
(KSC),” Steven Businger of the University of Hawaii, Honolulu, said. Nearly
75% of all space shuttle countdowns between 1981 and 1994 were delayed or scrubbed,
with about one-half of these due to weather.
|
|  |
| Image
2 | | Click
on image for animation. | The
new Global Positioning System (GPS) Lightning Index combines data on the amount
of water vapor in a cloud from a GPS receiver site with other meteorological data.
One GPS receiver is located at the KSC on Florida’s east coast.
“According
to the National Lightning Detection Network, the region where KSC is located has
one of the highest lightning flash densities in the country, which makes this
new Index extremely valuable,” said Robert A. Mazany, also of the University
of Hawaii.
|
|  |
| Image
3 | | | Mazany
and Businger worked with Seth Gutman at NOAA’s Forecast Systems Laboratory
in Boulder, Colo., and William Roeder at the 45th Weather Squadron, Patrick Air
Force Base, Fla., on the new GPS Lightning Index. Warm
moist air from the Atlantic Ocean and Gulf of Mexico provide the needed fuel for
near daily summer thunderstorms over Florida. Southwest airflow accounts for two-thirds
of the lightning strikes during the summer at KSC. Southwest flow collides with
the east coast sea breeze thus forcing the warm moist air to suddenly rise and
form thunderstorms over east central Florida. Then those same SW winds push the
thunderstorms eastward over KSC.
|
| | |
| Image
4 | | Click
on image for animation (16 MB) |
It’s
important to look at water vapor in thunderclouds because water and ice molecules
help to create the positive and negative charges in a thundercloud that generate
lightning. Warmer air tends to hold more water droplets. When there is enough
of a difference in the positive and negative charges in a cloud, lightning results. An
important weather challenge is to forecast lightning within a 20 mile radius of
the launch complexes, 1-8 hours before a first strike, depending on the operation
being supported. For instance a Shuttle landing requires a 90 minute lightning
forecast, whereas the movement of solid rocket boosters requires a four hour forecast,
and the movement of the Shuttle to the launch pad requires an 8 hour forecast.
Benefits of better forecasts include the safety of personnel and protection of
multi-billion dollar rocket launching systems, payloads, and supporting infrastructure.
Accurate lightning forecasts can save $1M by avoiding either a 24 hour launch
delay or the need to land the Space Shuttle at another facility and transport
it back to KSC.
|
|  |
| Image
5 | | Click
image for animation. (7.11 MB) |
Businger
said that data from the 1999 summer thunderstorm season was used to test the Index.
The Index combines four predictors, including a prediction tool of atmospheric
electric charge, the amount of water vapor detected in a cloud or air mass, the
change in the amount of that water vapor over 9 hours, and a scale called the
“K Index” that predicts how unstable the air will become. During
initial testing, the new index improved the lead-time for lightning strikes by
nearly 10% at the Kennedy Space Center. When Businger matched the index
with meteorological conditions from the summer of 1999, results revealed a 26%
decrease from the KSC's previous season’s false alarm rates.
|
|  |
| Image
6 | | | The
GPS Lightning Index provides useful guidance to forecasters for preparing lightning
forecasts, when combined with other resources such as radar and satellite data.
Further testing will continue to consider using the index to also forecast related
weather hazards such as heavy rain and flash flood events. The
article, “A New Lightning Prediction Index That Utilizes GPS Integrated Precipitable
Water Vapor,” appears in the October 2002 issue of the American Meteorological
Society’s Weather and Forecasting.
|
|  |
| Image
7 | | | This
research was supported by the U.S. Air Force and NOAA. Additional funding was
provided by NASA and the Department of the Navy, Office of Naval Research under
the Pacific STARNET program.
Back
to Top | 
