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PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE LITTLE ROCK AR
600 AM CDT TUE JUN 23 2009
...THE SCIENCE OF LIGHTNING...
THIS IS NATIONAL LIGHTNING SAFETY AWARENESS WEEK.
GOVERNOR MIKE BEBEE HAS DECLARED IT LIGHTNING SAFETY
AWARENESS WEEK IN ARKANSAS AS WELL. THE NATIONAL WEATHER SERVICE...
THE ARKANSAS DEPARTMENT OF EMERGENCY MANAGEMENT...THE ARKANSAS
DEPARTMENT OF PARKS AND TOURISM...THE U.S. ARMY CORPS OF
ENGINEERS...THE ELECTRIC COOPERATIVES OF ARKANSAS...AND ENTERGY
ARKANSAS INCORPORATED ARE SPONSORS OF THE WEEK IN ARKANSAS.
THE TOPIC FOR TODAY IS THE SCIENCE OF LIGHTNING.
THE POWER OF LIGHTNING.
EACH SPARK OF LIGHTNING CAN REACH OVER 5 MILES IN LENGTH...SOAR
TO TEMPERATURES OF APPROXIMATELY 50000 DEGREES FAHRENHEIT...AND
CONTAIN 100 MILLION ELECTRICAL VOLTS.
LIGHTNING IS A RANDOM...CHAOTIC...AND DANGEROUS FACT OF NATURE.
AT ANY GIVEN MOMENT...THERE ARE 1800 THUNDERSTORMS IN PROGRESS
SOMEWHERE ON THE EARTH. THIS AMOUNTS TO 16 MILLION STORMS EACH YEAR.
SCIENTISTS WHO STUDY LIGHTNING HAVE A BETTER UNDERSTANDING TODAY OF
THE PROCESS THAT PRODUCES LIGHTNING...BUT THERE IS STILL MORE TO
LEARN ABOUT THE ROLE OF SOLAR FLARES THAT IMPACT THE UPPER
ATMOSPHERE...THE ELECTROMAGNETIC FIELD OF THE EARTH...AND ICE IN
STORMS. WE KNOW THE CLOUD CONDITIONS NECESSARY TO PRODUCE
LIGHTNING...BUT CANNOT FORECAST THE LOCATION OR TIME OF THE NEXT
STROKE OF LIGHTNING FROM A STORM.
THERE ARE LIGHTNING DETECTION SYSTEMS IN THE UNITED STATES AND THEY
MONITOR AN AVERAGE OF 25 MILLION STROKES OF LIGHTNING FROM CLOUD
TO GROUND EVERY YEAR.
LIGHTNING HAS BEEN SEEN IN VOLCANIC ERUPTIONS...EXTREMELY INTENSE
FOREST FIRES...SURFACE NUCLEAR DETONATIONS...HEAVY SNOWSTORMS...AND
IN LARGE HURRICANES. HOWEVER...IT IS MOST OFTEN SEEN IN
THUNDERSTORMS.
A THUNDERSTORM FORMS IN AIR THAT HAS THREE COMPONENTS...MOISTURE...
INSTABILITY...AND LIFT...IN OTHER WORDS SOMETHING SUCH AS A COLD
FRONT WHICH CAUSES THE AIR TO RISE. CONTINUED RISING MOTIONS WITHIN
THE STORM MAY BUILD THE CLOUD TO A HEIGHT OF 35000 TO 60000 FEET...
OR 6 TO 10 MILES...ABOVE SEA LEVEL. TEMPERATURES HIGHER IN THE
ATMOSPHERE ARE MUCH COLDER...AND ICE FORMS IN THE HIGHER PARTS OF
THE CLOUD.
ICE IN THE CLOUD IS CRITICAL TO THE LIGHTNING PROCESS.
ICE IN A CLOUD SEEMS TO BE A KEY ELEMENT IN THE DEVELOPMENT OF
LIGHTNING. STORMS THAT FAIL TO PRODUCE QUANTITIES OF ICE MAY ALSO
FAIL TO PRODUCE LIGHTNING. IN A STORM...THE ICE PARTICLES VARY IN
SIZE FROM SMALL ICE CRYSTALS TO LARGER HAILSTONES...BUT IN THE RISING
AND SINKING MOTIONS WITHIN THE STORM...THERE ARE A LOT OF COLLISIONS
BETWEEN THE PARTICLES. THIS CAUSES A SEPARATION OF ELECTRICAL
CHARGES. POSITIVELY-CHARGED ICE CRYSTALS RISE TO THE TOP OF A
THUNDERSTORM...AND NEGATIVELY-CHARGED ICE PARTICLES AND HAILSTONES
DROP TO THE MIDDLE AND LOWER PARTS OF A STORM. ENORMOUS CHARGE
DIFFERENCES DEVELOP.
HOW LIGHTNING DEVELOPS BETWEEN THE CLOUD AND THE GROUND.
A MOVING THUNDERSTORM GATHERS ANOTHER POOL OF POSITIVELY CHARGED
PARTICLES ALONG THE GROUND THAT TRAVELS WITH THE STORM. AS THE
DIFFERENCES IN CHARGES CONTINUE TO INCREASE...POSITIVELY CHARGED
PARTICLES RISE UP TALLER OBJECTS SUCH AS TREES...HOUSES...AND
UTILITY POLES. IF YOU HAVE EVER BEEN IN A STORM AND HAD YOUR HAIR
STAND ON END...YOU HAVE SEEN THAT THE CHARGES CAN MOVE UP IN PEOPLE
AS WELL. THIS IS ONE OF NATURES WARNING SIGNS THAT SAYS YOU ARE IN
THE WRONG PLACE...AND YOU MAY BE A LIGHTNING TARGET.
THE NEGATIVELY CHARGED AREA IN THE STORM WILL SEND OUT A CHARGE
TOWARD THE GROUND CALLED A STEPPED LEADER. IT IS INVISIBLE TO THE
HUMAN EYE...AND MOVES IN STEPS OF LESS THAN A SECOND TOWARD THE
GROUND. WHEN IT GETS CLOSE TO THE GROUND...IT IS ATTRACTED BY ALL
THESE POSITIVELY CHARGED OBJECTS...AND A CHANNEL DEVELOPS. YOU SEE
THE ELECTRICAL TRANSFER IN THIS CHANNEL AS LIGHTNING. THERE MAY BE
SEVERAL RETURN STROKES OF ELECTRICITY WITHIN THE ESTABLISHED CHANNEL
THAT YOU WILL SEE AS FLICKERING LIGHTNING.
THUNDER.
THE LIGHTNING CHANNEL HEATS RAPIDLY TO 50000 DEGREES. THE RAPID
EXPANSION OF HEATED AIR CAUSES THE THUNDER. SINCE LIGHT TRAVELS
FASTER THAN SOUND IN THE ATMOSPHERE...THE SOUND WILL BE HEARD AFTER
THE LIGHTNING. IF YOU SEE LIGHTNING AND HEAR THE THUNDER AT THE SAME
TIME...THAT LIGHTNING IS IN YOUR NEIGHBORHOOD.
NEGATIVE LIGHTNING AND POSITIVE LIGHTNING.
NOT ALL LIGHTNING FORMS IN THE NEGATIVELY CHARGED AREA LOW IN THE
THUNDERSTORM CLOUD. SOME LIGHTNING ORIGINATES IN THE CIRRUS ANVIL AT
THE TOP OF THE THUNDERSTORM. THIS AREA CARRIES A LARGE POSITIVE
CHARGE...AND LIGHTNING FROM THIS AREA IS CALLED POSITIVE LIGHTNING.
THIS TYPE IS PARTICULARLY DANGEROUS FOR SEVERAL REASONS. IT
FREQUENTLY STRIKES AWAY FROM THE RAIN CORE...EITHER AHEAD OR BEHIND
THE THUNDERSTORM. IT CAN STRIKE AS FAR AS 5 TO 10 MILES FROM THE
STORM...IN AREAS THAT MOST PEOPLE DO NOT CONSIDER TO BE A LIGHTNING
RISK AREA. THE OTHER PROBLEM WITH POSITIVE LIGHTNING IS IT TYPICALLY
HAS A LONGER DURATION...SO FIRES ARE MORE EASILY IGNITED. POSITIVE
LIGHTNING USUALLY CARRIES A HIGH PEAK ELECTRICAL CURRENT...WHICH
INCREASES THE LIGHTNING RISK TO AN INDIVIDUAL.
FOR MORE ON THE SCIENCE OF LIGHTNING...
NATIONAL SEVERE STORMS LABORATORY...
WWW.NSSL.NOAA.GOV/PRIMER/LIGHTNING/LTG_BASICS.HTML
LITTLE KNOWN LIGHTNING FACTS...
WWW.LIGHTNING SAFETY.NOAA.GOV/LITTLE_KNOWN_FACTS.HTM
NWS COLORADO LIGHTNING PROGRAM...
WWW.CRH.NOAA.GOV/PUB/LTG.PHP
NWS JETSTREAM LIGHTNING TUTOR...
WWW.SRH.WEATHER.GOV/JETSTREAM/LIGHTNING/LIGHTNING_INTRO.HTM
NASA...
THUNDER.MSFC.NASA.GOV/PRIMER/
&&
ADDITIONAL INFORMATION ON LIGHTNING SAFETY CAN BE FOUND ON THE
INTERNET AT WWW.SRH.NOAA.GOV/LZK
$$
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