Our Window on Nature

. . . exploring the world around us

Anger of the Gods

Filed under: Weather — Lowell Christie -- April 15, 2006 @ 3:13 pm

Lightning - credit NOAAIn Colorado a tree exploded near our motorhome; shattered bark flew in every direction. In New Mexico thunderbolts crashed down on the ridge-top hiking trail that was our only route back to camp. In Florida lightning and thunder continued for seven hours until we gave up trying to get any sleep at all that night. Thunderstorms are a fact of life to the traveler – as many as 1800 of them rage somewhere on earth at any moment.

The light and sound shows that accompany thunderstorms center most commonly about the bulging waist of the planet, where a few tropical areas record 200 thunderstorm days every year. The noisemakers taper off as you move away from the equator, but only at the North and South Poles are you relatively safe from experiencing a thunderstorm.

By carefully choosing your travel route you can either avoid or seek out these violent weather patterns, depending upon your sense of adventure. Nowhere in nature is there a more awe-inspiring event than that found in the center of a storm. On this continent, storms decrease from south to north, and also from east to west. Typically, Florida reverberates from the rumble of a thunderstorm some 100 days of the year. Yet in Seattle, Washington, you would experience no more than five such storms during the same time period.

It is the sound effects that startle most people but, of course, thunder is only the voice of a storm. It’s the lightning that should cause you to tremble, for if you hear a crash of thunder you’re safe – the lightning has already struck elsewhere. Lightning is more common than generally believed, with a bolt striking the earth 100 times every second. If man could only harness its energy, there’s enough electricity in a typical strike to power a hundred lightbulbs for twenty-four hours.

Due to the speed of a lightning bolt, you see little of what occurs when lightning strikes. In reality, most of the action travels upward. First an electrical leader shoots down from the sky at over 240 miles per second, followed by a return stroke that moves several hundred times faster and contains most of the electrical charge.

Two types of lightning exist; hot and cold, although in this case cold is obviously a relative term. Cold lightning is of short duration, but contains a very high current. The lightning bolt that shattered the tree near us in Colorado was undoubtedly cold lightning, for it is known by its explosive effect. Hot lightning, in contrast, lasts longer, produces a lower current, and more frequently ignites a blaze.

Both types of lightning cause extensive property damage, and a strike from either type is potentially fatal. About 150 Americans are electrocuted by lightning each year – more than are killed by either tornadoes or hurricanes. But most of these fatalities are caused by people being where they shouldn’t – on a roof fixing a TV antenna during a storm; or taking shelter from the rain under the tallest tree in the area. One of the safest places to weather a thunderstorm is in a vehicle such as your motor coach. And from a safe place, a thunderstorm is a marvel to behold.

Three-quarters of the electrical energy contained in a bolt of lightning converts into heat, giving the center core of the lightning channel a temperature of 15,000 degrees centigrade. And it is the sudden increase in temperature of the air around it that produces the rumble of thunder. Super-heated air expands, moving faster than the speed of sound, causing a shock wave similar to that which occurs in an explosion. Not surprisingly, cold lightning, with its faster buildup of electrical energy, produces a louder thunder clap than hot lightning.

You can track the movement of a thunderstorm by knowing a few simple facts about weather and sound. As a child you learned to determine your distance from a lightning strike by counting the seconds between flash and crash. Traveling at a speed of 1090 feet per second, the sound of thunder originating from a strike one mile off reaches you in about five seconds. And under the right atmospheric conditions you can hear thunder from as far as fifteen miles away.

If you’ve wondered how a lightning bolt looks close up, but have been too smart to find out firsthand, here’s a safe way to examine one. Visit a sandy beach just after a thundershower, and look for “Petrified lightning” or fulgurites. When lightning strikes sand of the right composition, the grains fuse into a hollow tube. This tube extends into the sand, sometimes for as much as eight to nine feet – branching many times until it looks like the roots of a tree. Careful digging in soft sand can sometimes bring it out intact. Fulgurites occur in all parts of the United States, but few are ever recovered. Perhaps the reason is that in mythology only a god is allowed to hold a lightning bolt in his hand.

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