Thunder and Lightning

To understand lightning and thunderstorms, we need to start with the basics, the water cycle. Nature recycles its water through a process of evaporation and condensation.
1.The sun heats up the surface water
2.The water evaporates and rises into the air
3.The water vapor cools and condenses forming water droplets, which form the clouds.
4.When the water droplets become heavy enough, gravity pulls them back down again, completing the cycle.

As the water vapor condenses, it accumulates in the atmosphere as clouds until the droplets are large enough to feel the pull of gravity. Water vapor continues to rise, some water droplets are falling, some are changing phase (condensing) and they are all bumping into each other. With each collision, electrons are knocked off the molecules of water. As the water vapor rises, condenses and freezes, more electrons are knocked off. All the newly freed electrons sink to the bottom of the cloud giving it a negative charge.

The disparity in the charges causes an electric field to form. As with the charges, it is negative along the bottom of the cloud and positive along the top. As the collisions continue to knock electron free, the intensity of the electric field increases. It may become so intense that the electron on the earth's surface are repelled. (Opposites attract, like repel) The surface of the earth takes on a positive charge. All the charge needs now is a path. Once strong enough, the electric field will form that path.

The quiet rumble of thunder off in the distance will have most people scanning the skies looking for storm clouds. A storm is brewing. Is it moving toward you or away?

It wasn't until the 20th century that we truly understood what caused the thunder. It begins with the sudden thermal expansion (expansion due to heat) of the plasma in the lightning channel. For a fraction of a second, the air is superheated, reaching as high as 28,000 degrees Celsius. The superheated air moves faster than the speed of sound in the cooler air causing the shock wave we hear as thunder.

We see the flash of lightning, wait a beat, and hear the thunder. Light is electromagnetic radiation and travels at the speed of light. Sound travels much slower than that. You can get a rough estimate of how far away the lightning is by counting the seconds between the flash and the boom. Count the seconds and then divide by three and you will know approximately how far away it is in kilometers. If you want the distance in miles, divide the seconds by five.

The purpose of the lightning rod is not to "attract" lightning but to offer an easy path to the ground. The long, thin rod was originally developed by Benjamin Franklin in the late 1740's. It's a slender rod, around 2 inches in diameter and has a pointed end. The rod is connected to a thick copper or aluminum wire which in turn is attached to a grid buried in the ground nearby. When struck, the electrical current generated would travel down the wire and be safely dispersed in the ground.

Lightning tends to jump around when it strikes. Sometimes it strikes and then jumps around seeking an easier path to the ground. If the strike occurs near a lightning rod, the lightning will jump to it and be dispersed before more damage is done.

Lightning doesn't always follow a path to the ground. If two parts of a cloud are oppositely charged, the lightning will strike within the cloud. The entire cloud lights up. It is often referred to as sheet lightning. Lightning can arc from one cloud to another as well.

The lightning we're the most familiar with is called streak lightning, or forked lightning. It appears to shoot straight down forking just before it strikes. Whatever the name, it is as deadly as it is beautiful.

The safest place to be during a thunderstorm is in a large building, preferably one equipped with lightning rods. If you are in your car, stay there! It's far better than being out in the open. If you are caught outside, don't stand under a tree. It can act as a lightning rod and you would become part of the conduit. Another consideration is the heat generated by a strike. The boiling sap could cause the tree to explode.

Find a low-lying spot away from the trees or other potential strike zones. Keep your feet together, and hunker down. With your feet apart, discharging current could travel up one leg and down the other. By keeping your feet together, you're not giving it a path to follow. DO NOT lay down on the ground. A discharging flash would travel through your body as readily as it travels through the ground. Keep your head down and wait for the rainbow to appear.