What causes lightning?
As summer thunderstorms loom across the U.S., MNN sheds some light on lightning -- one of the deadliest and least-understood weather events on Earth.
By Russell McLendonWed, Jun 17 2009 at 8:30 AM EST
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Lightning is the weapon of choice for discerning deities. Whether you're Zeus, Thor or Tlaloc, there's no better way to assert your authority than smiting humans with thunderbolts.
Many people saw lightning this way for thousands of years, like a shock collar from the gods. The idea still comes up when someone says "may God strike me dead" to support a claim, and although scientists have learned a lot about weather and electricity in the past few millennia, lightning and other atmospheric electricity remains shrouded in mystery. Here's a rough sketch of what we do know:
How lightning works
As a summer thunderstorm soars over the landscape, it fuels itself by vacuuming up the warm, moist air below. Known as "updrafts," these vertical gusts are what create the storm cloud and what stir up the turbulent environment inside it where lightning is born.
Updrafts carry water droplets high into a thunderstorm, where they condense into clouds at the cooler altitudes around its peak. If there's enough humidity underneath the storm, it might billow into a towering monstrosity, launching some water droplets as high as 70,000 feet, miles above the freezing level. When these droplets freeze and fall back down, they collide with warmer droplets on the way, freezing them and releasing their heat. This heat keeps the surface of the falling ice slightly warmer than its surroundings, turning it into a soft hail known as graupel.
Although scientists still don't know how clouds generate the electrical charge needed for a lightning strike, many believe graupel is to blame. When it starts churning around the thunderstorm and crashing into other water droplets or ice particles, an odd thing happens: Electrons are sheared off the rising particles and collect on the falling ones. Since electrons are negatively charged, this leads to a cloud with a negative base and a positive top — like a battery. Unlike a battery, however, the cloud's electrical field is constantly being recharged by updrafts, which also continue stacking the storm taller and taller, pushing its positive top farther from its negative base.
Needless to say, this can't last. Nature abhors a vacuum, but she's no fan of electrical fields, either, usually releasing their energy any chance she gets. Still, Earth's atmosphere is a good insulator against such discharges, so an enormously powerful charge has to build up before it can overwhelm the uncooperative air. When that eventually happens, the resulting lightning bolt can have 100 million to 1 billion volts.
Lightning's first spark is an invisible streak of electricity, known as a "stepped leader," that begins forcing its way through the air in 50-yard bursts, looking for the path of least resistance between one charged region and the other. Once it connects with the opposite region's most convenient point, a glowing return stroke blasts back along the same path at 60,000 miles per second. A flash consists of one or up to 20 return strokes along the same lightning channel — usually about 1 to 2 inches in diameter — but it all happens faster than you can say greased lightning.
How thunder works
Thunder is the sound made by lightning. More specifically, it's the sound made by gases in the air exploding as lightning heats them to about 20,000 degrees Fahrenheit — three times hotter than the surface of the sun — in less than one second. The initial tearing noise is usually caused by the stepped leader, and the sharp click or crack heard just before the main crash of thunder is caused by the positive streamer up from the ground.
We can't hear thunder more than about 25 miles away from the storm, but the lightning flash may still be visible, since light travels faster and farther than sound. This type of seemingly silent lightning is often called "heat lightning," a common misnomer.
Lightning hits the planet about 100 times every second, or roughly 8 million times a day. While up to 80 percent of all lightning stays within the cloud where it formed, it's also well-known for venturing out, and comes in a wide range of styles, from spider and sheet lightning to blue jets, sprites and elves. Check out the following list for some of the highlights in Mother Nature's fireworks show:
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Comments
just wondering
06/25/2011 08:07 AM
What role does photosynthesis and zinc have in the process. When zinc is hit by sunlight it gains a positive charge. Plants use zinc in there growth. Any connection?
caleb
04/11/2011 10:41 AM
how does lightning form
edith1334
03/08/2011 16:39 PM
I wish they had graphics like this to make learning easier when I was in school. This is great.
Everyday Joe
06/01/2010 21:12 PM
Thank you for this information, I can use it for my research report.Really thank you it was good.:)
Lee Beckman LEED AP
06/19/2009 16:21 PM
So what is a way we can harness the energy from Lighting? I'm sure there's a safe way to capture all the electricity from lighting bolts and sell it as lighting power... how cool would that be to say your building project is powered by Zeus?
For green building education and consulting services: http://www.cleanedison.com
mhincha
06/17/2009 13:44 PM
My 7 year old is a weather fanatic and we just read this story together, he loved this! I have a feeling he's going to be quizzing grandpa now. :)
jim stevens
06/17/2009 13:29 PM
This describes how it works, lightning that is, but I love the mystery of it...and the timing between the boom and the flash.
Sean Roberts
06/17/2009 12:18 PM
Good to know. I think I'll go smite someone today.
Jackie S.
06/17/2009 11:59 AM
I didn't know 79% of lightning strikes were male victims. Yikes.
ecpdancer
06/17/2009 11:18 AM
I had no idea that lightning was that frequent all over the world. Incredible.
erin.p.fielding
06/17/2009 11:16 AM
or "intracloud" that is the coolest. I love it. I love it when you can watch it from a safe distance and just enjoy the show.
Missy
06/17/2009 11:14 AM
I love seeing how the different types of lightning work. Thank you! This is awesome. Lightning is still scary cool.
Elizabeth
06/17/2009 11:01 AM
One of my favorite things is sitting outside (safely on my porch) and listening to thunder, lightning and rain. Thanks for the explanation.
aliG
06/17/2009 10:56 AM
Now I know how thunder and lightning works-- thanks!
Sarah F.
06/17/2009 09:56 AM
Love the explainer. Any chance you know why lightning scares the bejeezus out of my dog?
Sam Talin
06/17/2009 09:49 AM
One word: Whoa.
Mark. S.
06/17/2009 09:36 AM
Whoa ... I had no clue that's what causes lightening. You'd think more people would know about this. As always, thanks for sharing these cool explainers.
