This enormous electrical discharge is
caused by an imbalance between positive and negative charges. During a storm,
colliding particles of rain, ice, or snow increase this imbalance and often
negatively charge the lower reaches of storm clouds. Objects on the ground, like
steeples, trees, and the Earth itself, become positively charged—creating an
imbalance that nature seeks to remedy by passing current between the two
charges.
A step-like series of negative
charges, called a stepped leader, works its way incrementally downward from the
bottom of a storm cloud toward the Earth. 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. The process forms a channel through which electricity
is transferred as lightning.
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.
Lightning is extremely hot—a flash
can heat the air around it to temperatures five times hotter than the sun’s
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.
Lightning is not only spectacular,
it’s 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.
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