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What Causes Lightning and Thunder?
Zap! You just touched a metal doorknob
after shuffling your rubber-soled feet across the carpet. Yipes! You've been
struck by lightning! Well, not really, but it's the same idea.
Your rubber-soled shoes picked up stray
electrons from the carpet. Those electrons built up on your shoes giving them a
static charge. (Static means not moving.) Static charges are always
"looking" for the first opportunity to "escape," or
discharge. Your contact with a metal doorknob—or car handle or anything that
conducts electricity—presents that opportunity and the excess electrons jump at
the chance.
lightning
What
causes lightning?
So, do thunderclouds have rubber shoes?
Not exactly, but there is a lot of shuffling going on inside the cloud.
Lightning
begins as static charges in a rain cloud. Winds inside the cloud are very
turbulent. Water droplets in the bottom part of the cloud are caught in the
updrafts and lifted to great heights where the much colder atmosphere freezes
them. Meanwhile, downdrafts in the cloud push ice and hail down from the top of
the cloud. Where the ice going down meets the water coming up, electrons are
stripped off.
It's
a little more complicated than that, but what results is a cloud with a
negatively charged bottom and a positively charged top. These electrical fields
become incredibly strong, with the atmosphere acting as an insulator between
them in the cloud.
When
the strength of the charge overpowers the insulating properties of the
atmosphere, Z-Z-Z-ZAP! Lightning happens.
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How
does the lightning "know" where to discharge—or strike?
The
electric field "looks" for a doorknob. Sort of. It looks for the
closest and easiest path to release its charge. Often lightning occurs between
clouds or inside a cloud.
But
the lightning we usually care about most is the lightning that goes from clouds
to ground—because that's us!
As the storm moves over the ground,
the strong negative charge in the cloud attracts positive charges in the
ground. These positive charges move up into the tallest objects like trees,
telephone poles, and houses. A "stepped leader" of negative charge
descends from the cloud seeking out a path toward the ground. Although this
phase of a lightning strike is too rapid for human eyes, this slow-motion video
shows it happening.
As the negative charge gets close to
the ground, a positive charge, called a streamer, reaches up to meet the
negative charge. The channels connect and we see the lightning stroke. We may
see several strokes using the same path, giving the lightning bolt a flickering
appearance, before the electrical discharge is complete
lightning and thunder
What
causes thunder?
In a
fraction of a second, lightning heats the air around it to incredible
temperatures—as hot as 54,000 °F (30,000 °C). That's five times hotter than the
surface of the Sun!
The
heated air expands explosively, creating a shockwave as the surrounding air is
rapidly compressed. The air then contracts rapidly as it cools. This creates an
initial CRACK sound, followed by rumbles as the column of air continues to
vibrate.
If
we are watching the sky, we see the lightning before we hear the thunder. That is
because light travels much faster than sound waves. We can estimate the
distance of the lightning by counting how many seconds it takes until we hear
the thunder. It takes approximately 5 seconds for the sound to travel 1 mile.
If the thunder follows the lightning almost instantly, you know the lightning
is too close for comfort!
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How
likely is lightning to strike a person?
Each
year, about 400 people in the U.S. are struck by lightning while working or
playing outside. About 50 people are killed and several hundred more are left
to cope with permanent disabilities.
The
summer months of June through September are the deadliest as far as lightning
is concerned. In 2022, 19 people died across the US from lightning strikes.
thunder
How
can I stay safe in a lightning storm?
Here
are some important rules to remember about lightning safety:
1. First
rule of lightning safety: No place outside is safe near a thunderstorm.
2. Plan
your outdoor activities so that you can get to a safe place in case a
thunderstorm develops.
3. Remember:
When thunder roars, go indoors! If you can hear thunder, the storm is near
enough to you to pose an immediate threat; after the thunder ends, wait 30
minutes before resuming outdoor activities.
4. If
thunder clouds are anywhere near, you should not be outside. Lightning can
travel long distances. It doesn't have to be raining overhead for lightning to
strike. Don't wait until the "last minute" to seek shelter. You don't
want to be a victim of a "bolt from the blue."
5. If
you are outside, go inside an enclosed building. You are also fairly safe in a
vehicle, if the windows are up and you do not touch any metal.
6. Once
inside a closed building, stay away from windows, showers, sinks, bath tubs,
and electronic equipment such as TVs, radios, corded telephones and computers.
7. If
you are caught outside and can't get to a safe place, there are things you
should avoid so that you don't increase the chance of being struck. Never take
shelter under a tree and stay away from other tall things like utility and flag
poles, but avoid open areas and high ground. Stay away from metal bleachers and
fences. Never lie on the ground as that increases the chances for being struck
by dangerous ground current.
8. Lightning
is an important part of weather forecasting. The Geostationary Lightning Mapper
instrument on the GOES-R series satellites can detect lightning activity over
nearly the whole Western Hemisphere.
9. Scientists
use data from GOES-R series satellites, along with data from the Lightning
Imaging Sensor on NASA's Tropical Rainfall Measuring Mission satellite, to
study lightning. This complete picture of lightning at any given time will
improve "now-casting" of dangerous thunderstorms, tornadoes, hail,
and flash floods.
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With my best wishes