Lightning lore, and a warning
Although we seem to have passed through the biggest barrage of thunderstorms of this spring storm season, with notably sunnier weather ahead, there are always risks of thunder and lightning in Maryland in the summertime. So, here are some lightning facts to know and use, courtesy of the National Weather Service in observance of Lightning Safety Awareness Week:
What are thunder and lightning, and how are they produced?
BY DEFINITION, ALL THUNDERSTORMS CONTAIN LIGHTNING. LIGHTNING IS A
GIANT SPARK OF ELECTRICITY THAT OCCURS WITHIN THE ATMOSPHERE OR
BETWEEN THE ATMOSPHERE AND THE GROUND. AS LIGHTNING PASSES THROUGH
THE AIR, IT HEATS THE AIR RAPIDLY TO A TEMPERATURE OF ABOUT 50,000
DEGREES FAHRENHEIT, ABOUT 5 TIMES HOTTER THAN THE SURFACE OF THE
SUN. DURING A LIGHTNING DISCHARGE, THE SUDDEN HEATING OF THE AIR
CAUSES IT TO EXPAND RAPIDLY. AFTER THE DISCHARGE, THE AIR CONTRACTS
QUICKLY AS IT COOLS BACK TO A NORMAL TEMPERATURE. THIS RAPID
EXPANSION AND CONTRACTION OF THE AIR CAUSES A SHOCK WAVE THAT WE
HEAR AS THUNDER (THIS SHOCK WAVE CAN DAMAGE WALLS AND BREAK GLASS).
So how is that giant electrical spark created?
AS A THUNDERSTORM CLOUD GROWS, PRECIPITATION FORMS WITHIN THE CLOUD
WITH MOSTLY SMALL ICE CRYSTALS IN THE UPPER LEVELS OF THE CLOUD, A
MIXTURE OF SMALL ICE CRYSTALS AND SMALL HAIL (GRAUPEL) IN THE MIDDLE
LEVELS OF THE CLOUD, AND A MIXTURE OF RAIN AND MELTING HAIL IN THE
LOWER LEVELS OF THE CLOUD. DUE TO AIR MOVEMENTS AND COLLISIONS
BETWEEN THE PRECIPITATION PARTICLES NEAR THE MIDDLE OF THE CLOUD,
THE VARIOUS PRECIPITATION PARTICLES BECOME CHARGED. THE LIGHTER ICE
CRYSTALS BECOME POSITIVELY CHARGED AND ARE CARRIED UPWARD INTO THE
UPPER PART OF THE STORM BY THE UPDRAFT. THE HEAVIER HAIL BECOMES
NEGATIVELY CHARGED IS SUSPENDED BY THE UPDRAFT OR FALLS TOWARD THE
LOWER PART OF THE STORM. THE END RESULT IS THAT THE TOP OF THE
CLOUD BECOMES POSITIVELY CHARGED AND THE MIDDLE AND LOWER PART OF
THE STORM BECOMES NEGATIVELY CHARGED.
NORMALLY, THE EARTH`S SURFACE HAS A SLIGHT NEGATIVE CHARGE;
HOWEVER, AS THE NEGATIVE CHARGES BUILD UP IN THE LOWER AND MIDDLE
PART OF THE STORM, THE GROUND BENEATH THE BASE OF THE CLOUD AND
IN THE AREA IMMEDIATELY SURROUNDING THE CLOUD BECOMES POSITIVELY
CHARGED. AS THE CLOUD MOVES, THESE INDUCED POSITIVE CHARGES ON
THE GROUND FOLLOW THE CLOUD LIKE A SHADOW. FARTHER AWAY FROM THE
CLOUD BASE, BUT UNDER THE POSITIVELY CHARGED ANVIL, THE NEGATIVE
CHARGE MAY BE FURTHER INDUCED.
IN THE INITIAL STAGES OF DEVELOPMENT, AIR ACTS AS AN INSULATOR
BETWEEN THE POSITIVE AND NEGATIVE CHARGES. HOWEVER, WHEN THE
ELECTRICAL POTENTIAL BETWEEN THE POSITIVE AND NEGATIVE CHARGES
BECOMES TOO GREAT, THE INSULATING CAPACITY OF THE AIR BREAKS DOWN
AND THERE IS A DISCHARGE OF ELECTRICITY THAT WE KNOW AS
LIGHTNING.
(SUN PHOTOS by Karl Merton Ferron 2004)
