Lightning

Lightning is the nasty offspring of the thunderstorm. Responsible for an average of 67 fatalities in the United States a year, lightning on average kills more people than hurricanes and tornadoes combined. Lightning is also responsible for leaving many more people with life long injuries such as memory loss, dizziness, and sleeplessness. Several thousand-forest fires a year in the United States can also be attributed to lightning strikes.

We are somewhat fortunate here in the Northeast in that this region is not affected by the volume of thunderstorms that other parts of the country experience such as Florida or the Midwest. However, Northeast thunderstorms can be every bit as vicious when they do occur, producing in some cases, one or two thousand cloud to ground lightning strikes per hour.

How Far Away is the Lightning?

The rule of thumb is, if you can hear thunder, you are in danger of being struck by lightning and should seek cover. You can determine how close lightning strikes are by counting the number of seconds between observing a flash and hearing the thunder. Thunder travels about one mile every five seconds, so count the seconds between the flash and the thunder, then divide that time by five to yield a distance in miles.

Lightning Safety

If You Are Caught Outside

Your chances of being struck by lightning are close to a million to one. In fact, most people that are struck are hit indirectly from the lightning charge traveling through the root system of a tree or the ground. Nevertheless, every year injuries and fatalities occur due to lightning. By following these safety guidelines it will increase your chances that you will not become the next lightning victim.

Stay away from high ground, tall trees, and metal structures. Lightning tends to strike objects that project above their surroundings. Your goal is to make yourself one of the shorter objects around. So, if you find yourself in a wide-open space such as a golf course or baseball field, seek shelter. If you can't find shelter and you feel a prickly feeling or observe your hair standing on end, it's a sign that static electricity is building up and that lightning may strike very close to you. In this case, immediately crouch or kneel using your arms to protect your head. DO NOT lie flat on the ground. The crouched position will lower you making you less of a target for a lightning strike. The downside of lying flat on the ground is that you expose more of your body area to a lightning charge that may be traveling through the ground from a nearby strike. By crouching you expose less body surface to a potential ground shock.

Also, if outside, avoid touching metal objects like fences, fishing rods, bicycles, or golf clubs, etc., which are good conductors of electricity.

Swimming

Water, because of its conductive nature, is an especially dangerous place to be in or around when lightning is occurring. A single lightning strike to a body of water allows the charge to spread out injuring or killing the fish or people that happen to be in the water at that location. Therefore, if swimming, whether it is a lake, pond, or backyard pool, get out of the water at the first sign of an approaching thunderstorm.

In A Boat

In a small boat, get to shore and to shelter immediately at the first sign of an approaching thunderstorm.

Where to Seek Shelter?

The best places to seek shelter are in closed buildings or in hard-topped metal automobiles. Cars offer excellent protection from lightning. The metal cage of a car will conduct electricity from a lightning strike around the outer shell, through the tires into the ground, away from you. A common myth is that it is the rubber tires that offer the insulation from lightning when it strikes a car, when in fact it’s the metal shell of the car that does all the work.

You want to stay away from open-air pavilions or similar structures. These types of structures may have roofs, but lightning can easily pass under the roof and strike.

Inside a Building

* Avoid anything that can conduct electricity, such as plumbing and electrical systems.

* If you have time prior to a thunderstorm's arrival, unplug expensive electrical appliances like computers and televisions. Surge protectors might not be enough to protect sensitive equipment, in some cases, if lighting strikes your home directly or even indirectly through the utility connections.

* STAY OFF THE PHONE. A lighting strike on a nearby line can produce an electrical surge though the phone line of your home and cause a shock that can be fatal. Cordless and cellular phones, however, are safer to use

* Stay away from open windows and doors until the storm has passed.

What Causes Lightning?

The cause of lightning is to this date not yet fully understood. The general thinking, however, is that electrification of a cumulus cloud is generated by the interaction of precipitation, both rain droplets and ice crystals, with other cloud particles as they are thrown around the thunderstorm vertically by the intense updrafts and down drafts. As ice crystals and water droplets are thrown up and down inside a thunderstorm they rub against each other, losing or gaining electrons and thus becoming positively and negatively charged ions. Heavier particles, such as hail, tend to gain electrons on their way down through the cloud giving the bottom of the cloud a net negative charge. Lighter ice crystals that remain suspended at the top of the cloud by the updraft, lose electrons to the heavier falling particles, and thus give the top of the cloud a net positive charge. The differences in electrical charges between the top and bottom of the cloud create up an electric field, which produces lightning. In essence, lightning is the instrument attempting to equalize the charges from the top to the bottom of the cloud.

The earth holds a net negative charge. However, the negative charge at the bottom of a thunderstorm cloud induces a positive charge on the ground under the storm. The differences in electric charge cause cloud to ground lightning, with the lightning bolt bringing down negative charge to the ground.

Structure of the Lightning Bolt

The typical cloud to ground bolt of lightning is composed of several elements. The first element of a lightning flash is called the stepped leader. The stepped leader zigzags downward from the cloud in intermittent steps of about 170 feet in length. The stepped leader's role is to bring down negatively charged particles from the cloud to the ground. As the stepped leader approaches the ground, a highly luminous positively charged return stroke rushes upwards into the cloud and dies out. If the cloud still has excess negative charge, a dart leader will follow the original path down to the ground initiating one or more return strokes. The typical lightning flash has three or four return strokes but up to twenty have been observed. The flickering appearance of a cloud to ground lightning flash is caused by the multiple return strokes. The process of the stepped leader creating the lightning channel, the return stroke illuminating it, the dart leader traveling down the channel followed by another return stroke, takes on the order of a tenth of a second.

Stepped leaders can be triggered to move upwards from the ground initiating a return stroke from the cloud. Upward moving stepped leaders initiate ground to cloud lightning flashes and are only accomplished by man made means. All natural lightning begins inside the cloud. Lightning also occurs within a thunderstorm cloud not involving the ground at all. Lightning not involving the ground is called intra-cloud lightning and is visible as long streaks of light through the cloud above the ground. Lightning also occurs between two clouds, called cloud to cloud lightning. In fact, intra-cloud and cloud to cloud lightning account for 80% of all lightning occurrences.

The Myth that is Heat Lightning

Many people believe there is a phenomenon called heat lightning. On hot evenings during the summer it's not uncommon to see a flash of lightning but not hear any thunder. Because thunder is not heard, many people attribute the lightning to the heat, thus the name. In reality, there is no such thing as heat lightning. The flash is simply a cloud to ground bolt or intra-cloud flash from a distant thunderstorm. The thunderstorm in this case is so far away that the thunder is not heard.

What Makes the Thunder?

Accompanying lightning are a variety of sounds, the ones you hear depend on your proximity to the bolt. If you are within about 100 yards of a lightning bolt you will hear a sharp click followed by a whip-like crack. Within about 600 yards, the sound can be described as more of an amplified tearing noise. These sounds are caused by the stepped leaders and return stroke. The most common sound, though is the rumble of thunder.

Thunder is caused by the explosion of hot gasses expanding from the lightning channel. The lightning channel is on average only a few centimeters in diameter. The gases in the tiny channel are very briefly heated to a temperature ranging from three to five times hotter than the sun. The superheated gases expand with explosive force, creating a shock wave which after a short time becomes the sound wave we hear as thunder. Because light travels so much faster than sound, the lightning flash always precedes thunder by several seconds.