As I sat here on a cloudy, soon-to-be rainy Thursday in October, forecasted to produce thunderstorms, I wondered what to write about when the idea struck me.
Lightning.
I am a child of teachers. Creative, passionate, dedicated and driven to help the students they taught; always fostering the curiosity within their students and their own children. I can vividly recall being woken up by thunderstorms as a child, going into my living room where there was a LARGE mirror and just watching the lightning flash and hear the thunder boom. I was never scared, rather I was fascinated by what I saw and heard! Since that time, lightning has mesmerized me. I'd sit and watch as long as the storm was over my home and to this day, I'll find any reason I can go sit on my balcony in a thunderstorm or find a place with a tall antenna, sit in my car with the hopes I'll see the antenna be struck. But that's one man's passion and the science behind lightning is incredible as my passion is deep, so let's learn something!
Lightning and thunder go hand-in-hand as I know you're aware of, but the science behind how the flash and the *boom* of thunder starts way up in the clouds and the air those clouds are formed in. As warm air rises and the clouds bubble up, any moisture starts to freeze and becomes crystalized; the theory states as these crystals fall due to their own weight, they hit other rising ice crystals, thus creating a negative charge at the base of the clouds. The picture below, from Weather Underground demonstrates this buildup of the charges within a thunderhead or Cumulonimbus cloud.
This charge builds and builds until it is too much for the cloud to "hold onto" and the excitement begins! Something called a "stepped leader" starts to form, and according to the National Weather Service's website, "Stepped leaders start to develop when charge differences in the cloud become too large. When this happens, the insulating capacity of the air breaks down and the negative charge starts moving downward." This stepped leader continues a tortured, jagged path, typically jumping 50 to 100 meters downward (164 to 328 feet) at a time until it meets up with something called an "upward streamer". While the (downward) stepped leader typically carries a negative charge, the upward streamer carries its opposite. Upward streamers are created from any tall structure or tree where a positive charge can accumulate during a storm. (Which is why if you feel your hair starting to stand up during a storm, you've become positively charged and you need to take action NOW so you don't get struck!) The stepped leader and upward streamer are "looking for" its opposite and once and upward leader and and stepped leader connect, the electrical charge that had been building up is released in a flash of lightning bolt and the clap of thunder!
Thanks to the clap of accompanying thunder, you can also learn roughly how far you are from the lightning strike. Once again, the National Weather Service offers their expertise: Since you see lightning immediately and it takes the sound of thunder about 5 seconds to travel a mile, you can calculate the distance between you and the lightning. If you count the number of seconds between the flash of lightning and the sound of thunder, and then divide by 5, you'll get the distance in miles to the lightning: 5 seconds = 1 mile, 15 seconds = 3 miles, 0 seconds = very close.
They also remind you to be in a safe space when counting, unlike what I like to do sometimes when I will be under my covered balcony. Which I admit is foolish and dangerous as there are many tall trees near my apartment building and any one of them could be struck. So please do not do as I do and have done. But this counting isn't just for cloud-to-ground lighting. The vast majority of lighting happens intracloud or simply up in the sky. But this can be more difficult because it is harder to see the bolt that is causing the *boom*.
Regardless of where the lighting ends, thunder follows it along. As previously stated, you can estimate the distance from the bolt to your location but what is the cause of the rumble that people like me enjoy so much? Simply, air. The temperature of an average lightning bolt is 50,000 degrees Fahrenheit! In case you're curious, that's five times hotter than the surface of the sun! This rapid heating causes the air to rapidly expand and contract equally quickly; an explosion of air! This rapid expansion and contraction caused a shockwave to form and propagate towards your ears. Now, depending on how far you are from the strike will also change what you hear in terms of the thunder. A loud *CRACK!* tells you what your body already did if you jumped when you heard that crack; that the strike was very close to your location, sometimes within a mile. The rumble that follows the main sound, is the expansion and contraction farther from your location, essentially traveling away from you and "up" the lighting bolt's main electrical channel. Regardless of direction, thunder will rumble from any lightning bolt as seen here in this upward lightning bolt!
Remember: When thunder roars, go indoors. If you can hear thunder you're close enough to be struck by lighting!
Thanks to slow motion videos we can now observe upward lightning in all its glory as well as the formation of stepped leaders as seen in these videos. Both videos are courtesy of Discovery Channel's Raging Planet series. This lightning is the opposite of cloud-to-ground lightning where positive charges build up on top of tall structures (as seen in the photo above). and discharges upward into the base of the cloud. Look closely in the photo and you will see the bolt is coming from a radio tower in the distance. The two videos below lend their collective insight.
As cool as lightning might be to you, there are LOTS of other things that lightning can and does produce that we cannot see because it happens too quickly for our eyes to perceive or are way too high in the atmosphere! There are electric disturbances that were only captured on film in 1994, called SPRITES, which stands for Stratospheric/mesospheric Perturbations Resulting from Intense Thunderstorm Electrification- I know, scientists and their acronyms, am I right?- or things called Blue Jets (no catchy acronym here), which form above the storm producing the lightning we've been discussing; they (blue jets) were only discovered in 1989! There are things called ELVES -get ready for another acronym. ELVES stands for Emissions of Light and Very Low Frequency Perturbations due to Electromagnetic Pulse Sources. I apologize, I don't create these names or acronyms, I just relay them.
These ELVES are large large disk-shaped areas that are thought to be generated by an electromagnetic pulse, or EMP. Typically these EMPs are associated with nuclear weapons tested in the atmosphere, only these are made from intense flashes of lighting! When you have a second, check out this short video taken by Thomas Ashcraft at the Heliotown Observatory in New Mexico. It shows these "holes" in the sky. Below are images and photos to help you understand the size and heights of some of these breathtaking phenomena!
From left to right: The first recorded image of a sprite (in 1994), a gigantic jet seen from the top of Mauna Kea and a diagram to help understand the scale associated with these ethereal phenomena.
There are other lightning-associated things worth discussing here, but I want you to follow your curiosity: Lightning that seems to make no thunder, Saint Elmo's fire, ball lightning and the world's longest lightning flash on record! These are all very real, electrostatic displays and all worth following up on.
While I am a passionate fan of weather, I am no expert and I feel that you need to listen to those who are. So, please, when you're done, visit the National Oceanic and Atmospheric Administration (NOAA) website to read their "5 striking facts versus myths about lightning you should know" and Lightning Safety Tips and Resources. And once more for those in the back...
Lastly and once again: When thunder roars, go indoors. If you can hear thunder you're close enough to be struck by lighting!