Each bolt a burning river

lightning

The oaks shone
gaunt gold
on the lip
of the storm before
the wind rose, 
the shapeless mouth 
opened and began
its five-hour howl;
the lights
went out fast, branches
sidled over 
the pitch of the roof, bounced
into the yard
that grew black
within minutes, except 
for the lightning–the landscape
bulging forth like a quick
lesson in creating, then
thudding away.
 

The opening lines of Mary Oliver’s poem “Lightning” are rapid-fire and breathless as the author describes the onset of a storm.  Summer is the time of year for thunderstorms, and in New England, we have been beset by one after another for days on end.  Do you remember being a child in a thunderstorm?  Perhaps you were afraid or enchanted or awed as the sky seemed to rip apart and you could imagine the earth itself trembling.  As adults, we have learned to stifle our most primal urges, yet a thunderstorm still gives us pause.  Step onto your porch or front step on a muggy afternoon just as those distant growls begin, smell the ozone and electricity in the air, and for just a moment, you can allow that same fear or enchantment or awe to take you over.

In order for a thunderstorm to form, there must be moisture and rapidly-rising warm air.  Since both moisture and warmth are required, thunderstorms occur most often in the spring and summer.  Once a thundercloud is formed, a charge separation develops within the cloud.  The inside of a cloud contains turbulent winds, water droplets, and suspended ice particles.  Drops of water in the bottom part of the cloud are lifted by updrafts to the colder top of the cloud, where they freeze.  At the same time, downdrafts within the cloud push the frozen ice and hail down from the top of the cloud.  As the falling ice meets the rising water, electrons are stripped off, creating a charge separation in the cloud.  The lost electrons accumulate at the bottom of the cloud, giving it a negative charge, while the newly positive unfrozen droplets continue rising, giving the top of the cloud a positive charge.

Charge distribution inside  a storm cloud.  (www.nssl.noaa.gov)

Charge distribution inside a storm cloud. (www.nssl.noaa.gov)

The cloud now has an electric field associated with it, one whose strength depends on the amount of charge in the cloud.  When the negative charges at the bottom of the cloud become strong enough, they actually repel electrons on the Earth’s surface, causing  a strong positive charge, which moves up to the top of the tallest objects. When the strength of the cloud’s negative charge overcomes the insulating properties of the surrounding atmosphere, lightning results.

The strong electric field in the cloud now creates a channel called a “stepped leader” which descends from the cloud seeking a path to the ground  (this happens faster than the human eye can see).  As it nears the ground, the negative charge is met by what’s called a “streamer” of positive charge that reaches upwards from the tallest object.  When the leader meets the streamer, a powerful electrical current begins to flow, and we see what we call “lightning” as  a return stroke barrels back up to the cloud at around 60,000 miles per second.  A lightning flash can contain as many as 20 return strokes.

Inside,
as always, 
it was hard to tell
fear from excitement:
how sensual 
the lightning’s 
poured stroke!  and still,
what a fire and a risk!
 
Slow motion lightning.  Note the stepped leader prior to the strike!

Slow motion lightning. Note the stepped leader prior to the strike!

Thunder is caused by the creation of lightning.  In a fraction of a second, the lightning channel heats the surrounding air to temperatures around 18,000 degrees Fahrenheit.  The heated air expands rapidly, and causes a sound wave called thunder.  The different sounds we hear in a thunderstorm correspond to the different stages of the lightning strike: the initial tearing sound is caused by the stepped leader, the ground streamer causes the click heard at close range, and the main crash of thunder is caused by the connection between the two and the enormous amount of energy generated in a lightning “bolt”.  The reason why our perception is that thunder occurs after lightning is because light travels so much faster than sound.

So what explains the way we react to a thunderstorm?  What is it about electricity, noise, and light that results in such a visceral response in many people?  It is possible that thunderstorms are merely the most common way many people come in contact with nature on an epic scale; natural events like tornadoes and hurricanes, while terrifying, are much more rare.  There is a name for a fear of thunderstorms: astraphobia.  It occurs in adults as well as children, and is listed among the top phobias in the US.  Sufferers experience symptoms of anxiety, as well as increased interest in weather forecasts.  So in some cases, people never feel entirely safe with this weather phenomenon.  Some never escape that childhood feeling of powerlessness.

Mary Oliver’s poem swiftly and beautifully leads the reader from the rapid buildup of a storm through to its violent height.  The speaker is both terrified and excited–electrified, one might say–by the power all around.  Once again, I am amazed at how much science can be divined by the pure emotion of a natural event.  Oliver’s sensitivity to this storm allows her the ability to describe both the internal and external chaos:

As always the body
wants to hide,
wants to flow toward it–strives
to balance while
fear shouts,
excitement shouts, back
and forth–each 
bolt a burning river
tearing like escape through the dark
field of the other. 
 

REFERENCES:

“Lightning,” by Mary Oliver.  Read it here.  

“Lightning Basics.” National Severe Storms Laboratory: NOAA.  Link.

“Thunderstorm Basics.” National Severe Storms Laboratory: NOAA.  Link.

“What Causes Lightning and Thunder?” SciJinks: NASA.  Link. 

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