Posted on August 18, 2018
Lightning (at a safe distance) is pretty cool. It has always fascinated me, partly for the ephemeral power that can explode a tree and disappear before my brain can register its existence, but also because lightning is a rare sight for these California eyes. What what exactly is going on in a lightning bolt? I thought you’d never ask….
The shocking truth about lightning
Lightning is an electrostatic discharge that equalizes negative/positive polarization between two objects. For example, when you get shocked touching the doorknob in your bedroom, you’ve been struck by your own personal lightning bolt. You got zapped because, courtesy of that carpet you just dragged your fuzzy slippers across, you picked up a few extra electrons that the doorknob was more than happy to relieve you of.
While the polarization process that happens in an electrical storm isn’t as thoroughly understood as the one in your bedroom, it’s generally accepted that a thunderstorm’s vertical, convective air motion shuffles electrons in the atmosphere. To jar your high school science memories, convection occurs when a fluid substance heats, becomes less dense, and rises until it cools and becomes dense enough to sink. (You initiate convection when you boil water.)
The is up/down circular flow of atmospheric convection happens when air near the ground warms, expands, and rises. The rising air carries water vapor; since cooler air can’t hold as much moisture as warm air, the ascending water vapor eventually condenses into clouds. The convective motion jostling the water and ice molecules inside the clouds strips the molecules of electrons. Electrons are negatively charged and more dense than the surrounding air; freed of their conventional bonds, these electrons fall earthward. Overhead, the clouds relieved of many electrons are suddenly positively charged, while the ground below has been rendered negatively charged by virtue of its new electron surplus.
Because nature abhors any imbalance, these opposite charges attract each other. The extreme polarization in a thunderstorm—positive charge at the top of the cloud, negative charge near the ground—is quickly (and violently) equalized: lightning! So I guess you could say that lightning is God’s way of telling Earth, “Stop being so negative!”
With lightning comes other atmospheric changes. The sudden infusion of a 50,000 degree electric charge displaces the surrounding air very suddenly, creating an audible compression wave that we know as thunder.
The visual component of the lightning bolt that caused the thunder travels to you at the speed of light, over 186,000 miles per second. But lightning’s aural component, thunder, only travels at the speed of sound, a mere 750 miles per hour (or so)—a million times slower than light.
Because lightning and its thunder are simultaneous, and we know how fast each travels, we can compute the lightning’s approximate distance. (Thunder’s speed varies slightly with atmospheric conditions; light’s speed is non-negotiable.) From our human perspective the lightning arrives instantaneously, but moving at 750 miles per hour, thunder takes around five seconds to travel a mile. So, dividing by five the number of seconds to elapse between the lightning’s flash and its thunder’s crash gives you the lightning’s distance in miles (divide the interval by three for the approximate distance in kilometers). For example, if ten seconds pass between the lightning and the thunder, the lightning struck about two miles away, fifteen seconds elapsed means it’s about three miles away, and so on.
This speed difference also explains why lightning comes and goes in milliseconds, while its thunder can rumble and roll for several seconds. Because a lightning bolt can travel many miles, the thunder from its nearest portions reaches you much sooner than its most distant components.
About this image
Each summer moisture from the Gulf of Mexico makes its way up into the American Southwest. The combination of moist air and extreme heat (to kick off convection) makes August ripe for thunderstorms at the Grand Canyon. For the last six years, Don Smith and I have scheduled two photo workshops hoping to photograph these thunderstorms and their effects (clouds, rainbows, and especially lightning).
Bit with unseasonably dry air in place, the forecast at the start of this year’s first Grand Canyon Monsoon workshop wasn’t especially favorable for lightning. I told the group during the orientation that I wasn’t concerned, that I’ve often seen forecasts like this change suddenly—then anxiously monitored every subsequent NWS forecast update with crossed fingers. In the meantime, we were all quite content photographing incredible smoke effects, courtesy of three nearby wildfires.
By the end of our second day I started seeing hints of moisture returning to the forecast toward the end of the workshop, with each forecast looking a little more promising than the one prior. By day four, the workshop’s final full day, I was downright optimistic.
We’ve always had better lightning success on the North Rim. Partly because the view faces south, the direction from which the storms tend to arrive, and partly because our cabins at Grand Canyon Lodge are right on the rim. Grand Canyon Lodge also has a pair of view decks, shielded by lightning rods, that are ideal for photographing lightning.
The lightning started firing early on our final evening. We all rushed to the rim, attached our Lightning Triggers, and pointed toward the most promising clouds. Much to my relief, it wasn’t long before everyone in the group had at least one lightning image, and most had many more than just one.
But feeling a bit greedy, with nice clouds overhead, and the smoke that had set up camp in the canyon for most of the week suddenly scoured by heavy rain, I realized that all we needed to ignite a sunset lightshow was a little sunlight. I glanced westward and saw signs of clearing. Dare I hope for a sunset to go with this lightning? As if by divine intervention, the sun emerged from the clouds just a few minutes before sunset, infusing the canyon and its diaphanous rain bands with light that started amber and reddened with each passing minute.
When the choice is between a (relatively) bland scene most likely to get lightning, and better a composition with just a slight chance for lighting, I usually take my chances and opt for the better composition. In this case the lightning had shifted a little north of the canyon, but I pointed my camera toward the better light over the canyon and crossed my fingers. So irresistible was the light that while waiting (and not wanting to change my composition and miss a lightning strike), I pulled my a7RII from my bag and clicked a couple of handheld frames due south, where no lightning was possible but the light was especially sweet. (Anyone who knows me will be shocked to hear that I took a picture without a tripod.)
Though several bolts fired during the five or so minutes before the sun disappeared, the one in this image was the only lightning I captured with the great sunset light. But all I wanted was one sunset strike, and I felt extremely lucky that it arrived just as the magenta glow reached its crescendo.
The lightning waxed and waned for several more hours. With the sun down the sky soon darkened enough for me to remove my Lightning Trigger and switch to long exposures in Bulb mode. I stayed until after 10:00, wrapping up with a couple of 20+ minute exposures that captured more than a dozen strikes each.