The Science of Lightning

By: Candice Sorensen Email
By: Candice Sorensen Email

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE TOPEKA KS
930 AM CDT TUE JUN 26 2007

...LIGHTNING SAFETY AWARENESS WEEK JUNE 24-30, 2007...

LIGHTNING SAFETY AWARENESS WEEK CONTINUES WITH A LOOK AT THE SCIENCE OF LIGHTNING.

HOW POWERFUL IS LIGHTNING? EACH BOLT OF LIGHTNING CAN REACH OVER FIVE MILES IN LENGTH...SOAR TO TEMPERATURES OF APPROXIMATELY 50,000 DEGREES FAHRENHEIT AND CONTAIN 100 MILLION VOLTS.

LIGHTNING IS A RANDOM...CHAOTIC AND DANGEROUS FACT OF NATURE. AT ANY GIVEN MOMENT...THERE ARE 1,800 THUNDERSTORMS IN PROGRESS SOMEWHERE ON THE EARTH. THIS AMOUNTS TO 16 MILLION STORMS EACH YEAR!

SCIENTISTS THAT STUDY LIGHTNING HAVE A BETTER UNDERSTANDING OF WHAT PRODUCES LIGHTNING...BUT THEY CANNOT FORECAST THE LOCATION OR TIME OF THE NEXT STROKE. LIGHTNING IS MOST OFTEN SEEN WITH THUNDERSTORMS.

THUNDERSTORMS DEVELOP WHEN THE ATMOSPHERE IS MOIST...UNSTABLE AND THERE IS A LIFTING MECHANISM (SUCH AS A COLD FRONT). AS THE AIR IS LIFTED AND IF IT CONTINUES TO RISE...THUNDERSTORM CLOUDS MAY REACH HEIGHTS OF 35,000 TO 60,000 FEET (6 TO 10 MILES) ABOVE SEA LEVEL.

WITH VERY COLD TEMPERATURES HIGH IN THE ATMOSPHERE...ICE FORMS IN THE HIGHEST PART OF THE THUNDERSTORM CLOUD.
ICE IN A CLOUD IS A KEY ELEMENT IN THE DEVELOPMENT OF LIGHTNING. IN A STORM...ICE PARTICLES VARY IN SIZE FROM SMALL ICE CRYSTALS TO LARGER HAILSTONES...BUT THE RISING AND SINKING MOTIONS WITHIN THE STORM CAUSES A SEPARATION OF ELECTRICAL CHARGES.

POSITIVELY CHARGED ICE CRYSTALS RISE TO THE TOP OF THE THUNDERSTORM AND NEGATIVELY CHARGED ICE PARTICLES AND HAILSTONES DROP TO THE MIDDLE AND LOWER PARTS OF THE STORM. ENORMOUS CHARGE DIFFERENCES DEVELOP WITHIN THE
THUNDERSTORM CLOUD.

A MOVING THUNDERSTORM GATHERS ANOTHER POOL OF POSITIVELY CHARGED PARTICLES ALONG THE GROUND THAT TRAVEL WITH THE STORM. AS THE DIFFERENCES IN CHARGES CONTINUE TO INCREASE...POSITIVELY CHARGED PARTICLES RISE UP TALLER OBJECTS SUCH AS TREES...HOUSES AND TELEPHONE POLES.

HAVE YOU EVER BEEN UNDER A THUNDERSTORM AND HAD
YOUR HAIR STAND UP? THIS IS ONE OF NATURE'S WARNING SIGNS THAT YOU ARE IN DANGER OF BEING STRUCK BY LIGHTNING.

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 IN 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 SEE AS FLICKERING LIGHTNING.

THE LIGHTNING CHANNEL HEATS RAPIDLY TO 50,000 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 THUNDER AT ALMOST THE SAME TIME...THE LIGHTNING IS IN YOUR NEIGHBORHOOD.

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. 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 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 INFORMATION ON THE SCIENCE OF LIGHTNING VISIT THE WEBPAGE AT THE NATIONAL SEVERE STORMS LABORATORY AT:
WWW.NSSL.NOAA.GOV/EDU/LTG (ALL LOWER CASE)

FOR MORE INFORMATION OR FOR LIGHTNING SAFETY INTERVIEWS...PLEASE CONTACT THE NATIONAL WEATHER SERVICE OFFICE IN TOPEKA KANSAS (785) 234-2592.


631 SW Commerce Pl. Topeka, Kansas 66615 phone: 785-272-6397 fax: 785-272-1363 email: feedback@wibw.com
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