the common expression, lightning can and often does strike the same
arcs from the top of a cloud to the horizon off the coast
of the Bahamas. Lightning that comes from the top of the cloud
can be positive lightning, which is rare but can be significantly
more powerful than more common negative lightning. It can
also strike farther from the cloud, up to 10 miles (16 kilometers)
(photograph by KARA SWANSON, MY
Lightning is an electrical
discharge caused by imbalances between storm clouds and the
ground, or within the clouds themselves. Most lightning occurs within
"Sheet lightning" describes a distant bolt that lights
up an entire cloud base. Other visible bolts may appear as bead,
ribbon, or rocket lightning.
During a storm, colliding particles of rain, ice, or snow inside
storm clouds increase the imbalance between storm clouds and the
ground, and often negatively charge the lower reaches of storm clouds.
Objects on the ground, like steeples, trees, and the Earth itself,
become positively chargedcreating an imbalance that nature
seeks to remedy by passing current between the two charges.
Lightning is extremely hota flash can heat the air around
it to temperatures five times hotter than the suns surface.
This heat causes surrounding air to rapidly expand and vibrate,
which creates the pealing thunder we hear a short time after seeing
a lightning flash.
101 Lightning strikes during thunderstorms kill more Americans
each year than either tornadoes or hurricanes.
TYPES OF LIGHTNING
Cloud-to-ground lightning bolts are a common phenomenonabout
100 strike Earths surface every single secondyet their
power is extraordinary. Each bolt can contain up to one billion
volts of electricity.
A typical cloud-to-ground lightning bolt begins when a step-like
series of negative charges, called a stepped leader, races downward
from the bottom of a storm cloud toward the Earth along a channel
at about 200,000 mph (300,000 kph). Each of these segments is about
150 feet (46 meters) long.
When the lowermost step comes within 150 feet (46 meters) of
a positively charged object, it is met by a climbing surge of positive
electricity, called a streamer, which can rise up through a building,
a tree, or even a person.
When the two connect, an electrical current flows as negative
charges fly down the channel towards earth and a visible flash of
lightning streaks upward at some 200,000,000 mph (300,000,000 kph),
transferring electricity as lightning
in the process.
Some types of lightning, including the most common types, never
leave the clouds but travel between differently charged areas within
or between clouds. Other rare forms can be sparked by extreme forest
fires, volcanic eruptions, and snowstorms. Ball lightning, a small,
charged sphere that floats, glows, and bounces along oblivious to
the laws of gravity or physics, still puzzles scientists.
About one to 20 cloud-to-ground lightning bolts is "positive
lightning," a type that originates in the positively charged
tops of stormclouds. These strikes reverse the charge flow of typical
lightning bolts and are far stronger and more destructive. Positive
lightning can stretch across the sky and strike "out of the
blue" more than 10 miles from the storm cloud where it was
THE IMPACT OF A LIGHTNING STRIKE
Lightning is not only spectacular, its dangerous.
About 2,000 people are killed worldwide by lightning each year.
Hundreds more survive strikes but suffer from a variety of lasting
symptoms, including memory loss, dizziness, weakness, numbness,
and other life-altering ailments. Strikes can cause cardiac arrest
and severe burns, but 9 of every 10 people survive. The average
American has about a 1 in 5,000 chance of being struck by lightning
during a lifetime.
Lightning's extreme heat will vaporize the water inside a tree,
creating steam that may blow the tree apart. Cars are havens from
lightningbut not for the reason that most believe. Tires conduct
current, as do metal frames that carry a charge harmlessly to the
Many houses are grounded by rods and other protection that conduct
a lightning bolt's electricity harmlessly to the ground. Homes may
also be inadvertently grounded by plumbing, gutters, or other materials.
Grounded buildings offer protection, but occupants who touch running
water or use a landline phone may be shocked by conducted electricity.