18 Miles

by Christopher Dewdney

  As permanent residents of Earth, we don’t have the option of moving elsewhere. For better or worse, we’re stuck here. And it could be worse. Take Jupiter, where millions of electrical storms rage daily. In fact, Jupiter’s Great Red Spot is actually a stupendous, stationary hurricane with a 19,000-mile-wide eye that has raged for at least 300 years. Saturn is little better. When Voyager passed by in 1981, it picked up static from a giant equatorial thunderstorm 37,000 miles wide, with wind speeds that clocked in at over 932 miles per hour. We’ve got it easy.

  Even so, earthly storms can pack a punch. A typical thunderstorm produces several hundred megawatts of electrical power, enough to supply all of the U.S. for 20 minutes — or by a more violent yardstick — it’s equivalent to the energy released by an atomic bomb. So when a storm looms on the horizon, all we can do is batten down the hatches or, in the case of tornadoes, duck into a storm cellar if we have one. But how do storms begin? Why are they so violent? The answer has a lot to do with heat. Tornadoes, hurricanes, typhoons and most thunderstorms need warm weather to spawn, as well as moisture, and a lot of it. Storms are clouds showing their muscle.

  A summer thunderstorm starts life as a cumulus cloud cruising over fields and rivers and lakes. It’s a case of wandering lonely as a cloud, certainly, but a cloud with megalomanical tendencies. The fledgling storm feeds on thermal updrafts, sucking up moisture like a vacuum cleaner, and, as it drifts, it inflates until it reaches the next stage of its evolution, transforming into a cumulus congestus. This is a sort of adolescent cumulonimbus that can reach heights of 6,500 feet. Now the first drops of rain begin to fall.

  At this point, two things happen. The rising humid air that initially puffed up the cloud now accelerates into an industrial-scale updraft, while rainy downdrafts begin shunting cooler air downward at the same time. All this commotion creates friction, particularly at the atomic particle level, and static electricity begins to build up charges in the cloud. Our cumulus congestus has become a full-fledged cumulonimbus and now has electrical potential — a positive charge in the cold heights of the cloud and a negative charge in the warmer regions closer to the Earth. Zeus’s arsenal. These charges build in strength until a glowing stream of electrons irresistibly bridges the gap. Zeus hurls a bolt.

  But air is not a good conductor, even with billions of volts and hundreds of thousands of amperes at a bolt’s command. The atmosphere might as well be a thick rubber sheet. Lightning needs help, and Joseph Dwyer, a physicist from the University of New Hampshire, thinks it might come from cosmic rays — high-energy particles moving at the speed of light out of the cores of exploding stars. Our planet is continuously bombarded by millions of cosmic rays; as they streak through the atmosphere, they leave a trail of electrically charged particles. These brief channels are what lightning rides to the ground, and sometimes into it. Lightning often penetrates yards into sandy soil, fusing the mineral particles together into solid, wiggily tubes called fulgurites, or lightning stones.

  Lightning

  “Thunder is good, thunder is impressive;

  but it is lightning that does the work.”

  Mark Twain

  My childhood home in southwestern Ontario was on the crest of a ravine that opened westward over an expanse of oxbow lakes. It was a perfect vantage for watching summer storms. My mother, born in Medicine Hat, Alberta, had prairie experience with tornado weather, and on hot, humid days with a strong southwest wind, she would tell my brothers and me to keep an eye on the western horizon starting around four in the afternoon. A severe storm could blow up quickly and it was best to have a safe place handy to wait it out. I think that, like me, my mother privately enjoyed thunderstorms.

  If a tornado actually touched down, my mother told us the most protected place in any building was the southwest corner, which made sense — tornadoes usually track from southwest to northeast. Despite her admonitions, when the weather was right I prayed for storms.

  There was a delirious excitement that came with the approach of a cumulonimbus cloud, particularly if it was a “line storm.” These storms were always big and had a characteristic shape. Meteorologists now call them squall lines. There’s a wonderful oil painting of one by the American painter John Steuart Curry, titled simply The Line Storm. It depicts a summer afternoon in the American Midwest, grain fields, tree-lined country roads, barns and a windmill, above and behind which looms the black, bowl-shaped front of a line storm rising above the horizon. The storm occupies the upper half of the painting. In the foreground is a horse-drawn hay wagon racing to find shelter. Curry’s painting captures the electric mood of apprehension at the imminent approach of unknown violence.

  During the summer, we’d get our share of regular thunderstorms, but we were also hit by line storms, like the one in Curry’s painting. These would strike, just as Mother predicted, around four or five in the afternoon. The hot wind would die suddenly, and then the curved line of the storm would begin rising above the western horizon like the leading edge of some inconceivably huge flying saucer. Underneath the projecting upper rim was an ominous blue-black zone that widened as the storm approached. You could see lightning flickering in there, and as the storm grew nearer still, you’d hear the first rumbles of thunder.

  I’d run to my vantage on the edge of the ravine where I loved to watch the edge of the storm slide overhead, the point of no return. On the street behind me, adults rolled up their car windows and snatched down any laundry still out on clotheslines while the thunder got louder and the flicker of lightning started to cast sudden, alarming shadows. This was drama. Then it got darker still, and the streetlights came on, and the sky took on an eerie purple or greenish cast. Invariably, there would be a close lightning strike where you could see the whole bolt, followed immediately by a loud crack of thunder. About a mile distant, in the darkness under the storm, the rain curtain approached just behind the lashing treetops. The squall line was coming. I could count down from that point, about 20 seconds, before the wind hit and leaves and small branches started flying. But I stood my ground at the top of the ravine. It wasn’t until the first big drops started to fall that I retreated to my house in time to avoid being completely drenched.

  Viewing the rest of the storm from the relatively safe vantage of my parents’ glass-walled sun porch, I’d watch the street turn into a river. Lightning was now constant, and the windows of the porch rattled with the thunder. Neighbors caught in the downpour splashed along with their jackets pulled over their heads. Soaked to the bone, as we used to say. I thought of monsoons in southern India, the tropical foliage, the wet arms and legs. Then a terrific flash-bang, very close. Did that hit a house in the neighborhood? I would try to figure out how far away the center of the storm was by using a technique my father once taught me when we were camping.

  Temperatures at the core of a lightning bolt can be as high as 30,000°C, or six times hotter than the sun’s surface, instantly vaporizing the narrow tunnel of air it travels down. The surrounding air is pushed outward by the heat, and the shockwave travels at the speed of sound until it reaches our ears as thunder. By counting the seconds between the flash and the thunder, every five seconds being equivalent to a mile, you can determine how far away the lightning strike is. A direct, vertical cloud-to-ground strike (or a “CG” as storm chasers like to call it) will produce a single loud clap of thunder, whereas branched lightning, sometimes completely confined to clouds, creates long, rolling peals of thunder. With a stopwatch and a little experience, you can map out the height and length of branched lightning bolts. But this is academic if you are camping and prone to a little anxiety about storms. The shortening seconds between flash and thunder only increase your panic. Who knows where the next bolt will strike as the center of the storm gets closer?

  Lightning is dangerous. On average, lightning kills 16 people a year in Canada and 95 in the United States. It doesn’t seem like a lot compared to automobile accidents or gun viole
nce, but it is sometimes a gruesome way to go. A friend of mine attending an equestrian event on a cloudy summer afternoon was close to another rider when she was struck by a rogue bolt of lightning. The horse survived but the rider didn’t. What my friend couldn’t get out of her mind, for weeks afterward, was the smell. “Like a roast,” she said. And it wasn’t even raining.

  If you are caught out in the open by an electrical storm, never take shelter under a single tree. A thicket of short trees of uniform height theoretically offers better protection, but lacking that it’s best to crouch with your feet and knees together in the open. Some guides say it doesn’t matter if you stand or crouch, but I say crouch because you have a lower profile that way. I’ll tell you why.

  Years ago, I was in a log cabin in northern Ontario that was struck by lightning during a pop-up storm that had come in fast over the lake. The concussion of thunder (which must have originated within the cabin) was like an explosion. It deafened me. Then I remember that the air was suddenly hazy, my ears were ringing and one of the logs in the wall had exploded. I waited out the rest of the storm outside the cabin. It was irrational, but I was convinced that lightning would strike there again.

  The cabin survived, but, upon inspecting it half an hour later, it was remarkable to see the paths of the various tendrils of lightning. Besides scorching and stripping a spiral of wood from a log in the wall, it had splintered floorboards and even run through the metal wires on a dartboard, jumping from there to split a mercury thermometer sitting in a jar beneath, a yard from where I was standing. It was sobering. I had been lucky.

  My childhood intoxication with electrical storms changed that day. Now, I really don’t think you want to be any closer to lightning than you have to be, so I say crouch if you’re caught in a field. Why with knees and feet pressed together you might ask? Because if your feet are even slightly apart, it will tempt the lightning to pass through your body. Flesh and blood are a much better conductors than grass and soil. The interiors of cars are safe, because the metal body conducts the strike around the occupants and to the ground. Large enclosed spaces are still the safest place to be during electrical storms. In the Middle Ages, it was thought that a Yule log kept in the fireplace during the summer warded off lightning strikes, but these days just staying off a landline telephone during a storm will suffice. Curiously enough airplanes are also generally safe, even if they sustain a direct strike.

  “All night sheet lightning quaked sourceless to the west beyond the midnight thunderheads, making a bluish day of the distant desert, the mountains on the sudden skyline stark and black and livid like a land of some other order out there whose true geology was not stone but fear.”

  Cormac McCarthy

  Earth plays host to about 44,000 thunderstorms daily, which means that it is being struck by lightning around 100 times a second. Lightning comes in a plethora of shapes and sizes — heat lightning, spider lightning and even hot and cold lightning. I liked the idea of cold lightning when I first heard about it, imagining a cool neon bolt with thunder and no heat, but that isn’t anywhere close to what the term means. The difference between hot and cold lightning turns out be the number of return strokes, and their duration, in a single lightning bolt. It all becomes visible when lightning is slowed to a crawl.

  Filmed in extreme slow-motion, lightning doesn’t even look like lightning, and there is way more going on than you’d think. The ghostly, sparking tendrils of the main leader snake randomly in all directions as it approaches the ground, exploring the potential of the space around the bolt. The tendrils that don’t connect fizzle out while the one that does touch the ground suddenly turns white hot as the entire billion-volt charge zooms down the corridor opened up by this single successful filament. Then a brief pause of darkness and suddenly again the same shape is illuminated as a return charge races up to the cloud. If this happens just once, it’s cold lightning. But if several strokes of longer duration follow the same path upward and downward, it’s hot.

  Return strokes were first photographed in 1902 when Sir Charles Vernon Boys used a special camera he’d invented that used revolving film to capture lightning bolts in a time “smear.” When the moving film is exposed to the light from a single lightning strike, it spreads it out in time so that the resulting photograph of the various return strokes looks like after-images of the same bolt repeated side by side. More return strokes means longer duration and more potential for whatever the lightning hits, be it dry grass or wood, to catch fire. That’s why it’s called hot lightning.

  Hot lightning is not to be confused with heat lightning, the silent lightning that accompanies storms during heat waves. Years ago, during an early summer heat wave, I witnessed several nights of magical heat lightning in the skies over my hometown. For two or three evenings one week, the night sky would fill with low, rainless storm clouds and then, for hours on end, there would be a spectacular light show of spider lightning (lightning with many branches and channels that sometimes recombine) so prolific it looked like electric lacework stitching the clouds. What made it eerie was that the entire spectacle was completely silent.

  It would be remiss of me not to mention that what I witnessed in my hometown is officially impossible. The meteorological consensus on heat lightning is that it’s merely lightning that is too distant to hear the thunder. But much of the heat lightning I saw was directly overhead, less than a mile distant.

  Riders on the Storm:

  Sprites, Blue Jets, ELVES, Pixies, Gnomes and Trolls

  But the story of lightning gets stranger and stranger. There is another form of lightning, one that doesn’t jump from cloud to cloud or cloud to ground. Instead it reaches straight up to the heavens. High above the fury of violent thunderstorms, in the calm, sparse air of the stratosphere and beyond, ghost riders flicker and dance like vanishing hallucinations.

  Some of these apparitions, pale as faint red neon signs and shaped like jellyfish, appear fleetingly, as if momentarily lit up by a stray flash. Others look like blue rays speeding upward like rockets from the top of an anvil cloud. A third, more massive type illuminates the lower ionosphere in a pale 124-mile-wide pink donut. All are ephemeral.

  These electrical specters were discovered accidentally a little over two decades ago by scientists from the University of Minnesota. On July 6, 1989, they were testing low-light video cameras at night and by chance caught an image of a peculiar glow above a midwestern storm. Later analysis proved the image to be no optical flaw; something extraordinary had appeared in the sky over the storm clouds.

  These aerial lights are known, rather poetically, as sprites and blue jets. (Yes, scientists can be whimsical too.) As it turns out, there had been previous eyewitness accounts of these strange coruscations. Sprites have been dancing above storms for millions of years, so it stands to reason that a few humans had already seen them. It’s just that these accounts were so sporadic no one thought to investigate them.

  The first written record of what was most likely a blue jet was published in 1730 by Johann Georg Estor, a German legal theorist, in the second volume of his Neue Kleine Schriften. He described climbing a mountain in the Vogelsberg up through a thunderstorm. When he emerged from the top of the storm cloud and looked down on it, he saw something he’d never seen before — a streak of lightning shooting straight up into the clear sky above the storm.

  Since Estor’s sighting, there have been handful of accounts by various observers, of both blue jets and sprites, but it took the University of Minnesota video to get the ball rolling. Over the past two decades, many more of these enigmatic lights have been observed, and several distinct types have emerged from the research. The first, witnessed by the night camera in 1989, was named a sprite by the two leading experts on this form of lightning, Davis Sentman and Eugene Wescott of the University of Alaska at Fairbanks. Their folkloric nomenclature stuck, and, as a result, the names for upper atmosphere lightning manifestations sou
nd more likely to appear on a page in The Lord of the Rings than a scientific treatise.

  Even their rival, the meteorologist Walter A. Lyons, fell in line. His scientific label for the pink donut lightning he discovered was emissions of light and very low frequency perturbations from electromagnetic pulse sources, or ELVLFPFEPS, but he shortened it to ELVES. Since then, other mythological creatures have been added to the family — pixies and gnomes (briefly glowing balls of light on the upper edges of storm clouds) and TROLLs (transient red optical luminous lineaments), the red tendrils that hang down from sprites.

  All of these ethereal forms of lightning are completely unlike the mighty bolts that singe the clouds beneath them. They are radiant plasma, more like the glow within a fluorescent light. But they are colossal. Hovering between 25 to 56 miles above the Earth, sprites are often 31 miles tall, and some ELVES are more than 245 miles in diameter. What they lack in voltage, they make up for in pure scale, dwarfing the storm clouds that birthed them. Sprites are not completely without sting, however. The sudden electrical failure of an upper atmosphere NASA probe on June 6, 1989, has been retroactively linked to damage from a sprite. Come to think of it, was William Rankin’s inexplicable engine failure over the thunderstorm in North Carolina due to a blue jet overloading all the electrical cables in his aircraft? We’ll never know.

  Great Balls of Fire

  Just after midnight, on March 19, 1963, Eastern Airlines flight 539 was en route from New York City to Washington, D.C., when it encountered a turbulent thunderstorm. The passengers barely had time to fasten their seatbelts before a sudden burst of light and a terrific thunderclap shook the plane. Moments later, a glowing sphere, about the size of a volleyball, floated out of the pilot’s cabin and drifted down the aisle to the back of the airplane where it disappeared.