MNN.COM > Earth Matters > Translating Uncle Sam

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 McLendon
Wed, Jun 17 2009 at 9:30 AM EST
Read more: SEVERE WEATHER, WEATHER & CLIMATE

 
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.
 
For thousands of years, many people saw lightning this way, like a shock collar from the gods. The idea still comes up when someone offers "may God strike me dead" to bolster a claim, and although we've learned a lot about weather and electricity in the past few millennia, lightning and other types of atmospheric electricity remain shrouded in mystery. Uncle Sam's scientists are hard at work, though, and they've pieced together a rough idea of how it all goes down.
 

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:
 
KEEP READING: Types of lightning >


CLOSE link:

Comments(15)

Sort by:
Posted By Kamila - Sat, Feb 20 2010 at 12:47 AM EST

nice work

I like your post its quite informative and i love to visit you again as you have done a wonderful job. i love to bookmark this site and would send it to other friends to read it and visit it to get upto date and quite interesting information 70-620 exam, i will be here again as i get some time from 70-630 exam services because they make me little busy, but i would love to stuck here again ccie written exam preparation. Thanks for sharing nice information with.... More

Posted By Lee Beckman LEED AP - Fri, Jun 19 2009 at 4:21 PM EST

Lightness

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

Posted By Leadscribe - Thu, Jun 18 2009 at 5:33 AM EST

How uncannily coincidental

A thunderstorm started here while I was reading this, and I could see flashes of lightning out the window. :O

http://www.leadscribetranscription.com

Posted By Melissa Hincha-Ownby - Wed, Jun 17 2009 at 1:44 PM EST

My 7 Year Old Loved This

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. :)

Posted By jim stevens - Wed, Jun 17 2009 at 1:29 PM EST

Bolts of lightning

This describes how it works, lightning that is, but I love the mystery of it...and the timing between the boom and the flash.

Posted By Sean Roberts - Wed, Jun 17 2009 at 12:18 PM EST

Lightning

Good to know. I think I'll go smite someone today.

Posted By Jackie S. - Wed, Jun 17 2009 at 11:59 AM EST

lightning strikes

I didn't know 79% of lightning strikes were male victims. Yikes.

Posted By EastSideChick - Wed, Jun 17 2009 at 11:18 AM EST

100 times every second?

I had no idea that lightning was that frequent all over the world. Incredible.

Posted By GreenErinF - Wed, Jun 17 2009 at 11:16 AM EST

sheet lightning

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.

Posted By Missy - Wed, Jun 17 2009 at 11:14 AM EST

Lightning is SO cool!!!

I love seeing how the different types of lightning work. Thank you! This is awesome. Lightning is still scary cool.

Posted By Elizabeth - Wed, Jun 17 2009 at 11:01 AM EST

I love Lightning

One of my favorite things is sitting outside (safely on my porch) and listening to thunder, lightning and rain. Thanks for the explanation.

Posted By aliG - Wed, Jun 17 2009 at 10:56 AM EST

Great article

Now I know how thunder and lightning works-- thanks!

Posted By Sarah F. - Wed, Jun 17 2009 at 9:56 AM EST

Lightning strikes

Love the explainer. Any chance you know why lightning scares the bejeezus out of my dog?

Posted By Sam Talin - Wed, Jun 17 2009 at 9:49 AM EST

Freaky lightning

One word: Whoa.

Posted By Mark. S. - Wed, Jun 17 2009 at 9:36 AM EST

Lightning

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.

Add your comment

You can’t fool Mother Nature
This question is for testing whether you are a human visitor and to prevent automated spam submissions.
Image CAPTCHA

ADVERTISEMENT

SHEA'S RECENT POSTS

POLITICS, ENERGY, AND OUR EARTH'S RESOURCES
+ add this to my site

MNN ORIGINALS

Not sure which green way is best? Get answers from our experts.

We've got a new contest coming soon.

Government data you need to know, in a way you can understand.

Check out eco-photos of the week, top 10 lists and more.

Learn more about everything from acid rain to wildlife.