The awe-inspiring, often destructive power of lightning has instilled both fear and fascination in mankind for eons.
Before science discovered how and why lightning occurs, humans were convinced there was a mythological or theological explanation for this breathtaking force of nature.
The first structured scientific study of lightning was conducted by Benjamin Franklin during the second half of the 18th century.
Franklin postulated that clouds are electrically charged, ergo, lightning was an electrical charge. He originally proposed an experiment to test his theory by placing an iron rod next to a grounded wire, which would be secured by a nearby wax candle. He surmised that if the clouds were indeed electrically charged, electricity would jump between the iron rod and the grounded wire. If the clouds were electrically charged as he expected, then sparks would jump between the iron rod and the grounded wire.
Franklin published a proposed experiment in 1750,l whereby a kite would be flown in a storm to attract lightning. By the summer of 1752, it is thought that Franklin conducted the experiment during a large storm in Philadelphia.
Franklin also concluded that the lower part of the thunderstorm was generally negatively charged. It should be noted that it is unlikely that lightning actually struck the kite, which would have likely resulted in Franklin’s. Death. The plausible scenario that is the kite attracted nearby ambient charges.
Modern studies began with the Scottish physicist and meteorologist Charles Thomas Rees Wilson was the first scientist to use electrical field measurements, who was the first to use electric field measurements to approximate the composition of electrical charges involved in lightning discharges. Applying what he had learned from his studies of thunderstorms, Wilson divided a method of protecting British war balloons from lightning. In 1956, he published a theory of thunderstorm electrical energy. Today, many high-tech tools and advanced computer software are used to detect and analyze lightning.
What is lightning?
The short answer is that lightning is a sudden electrical discharge that occurs during a thunderstorm. In the initial stages of lightning being produced, air serves as an insulator between the negative and positive charges in the cloud and the charges between the ground and the cloud.
Intra-cloud lightning takes place between oppositely charged regions of a cloud; cloud-to-cloud lightning occurs between one thundercloud and another; and cloud-to-ground lightning, which primarily begins in the thundercloud and terminates on an Earth surface, however this type may also occur in the reverse direction which is called ground to cloud lightning.
How is lightning formed?
Storm clouds are composed of billions of water molecules and ice crystals that begin moving rapidly, faster and faster. As the water molecules collide, electrons are dislodged, creating separation of charges. The displaced electrons fall to the lower portion of the cloud, thus producing a negative charge on that part of the cloud. Consequently, clouds become charged, with the upper portion of the clouds typically becoming more positive and the lower section becoming more negative.
Because positively and negatively charged objects attract, and conversely like charges repel, the negative end of the cloud, being lower, is closer to the ground and repels negatively charged molecules on the ground. This repulsion results in a strong positive charge on the Earth’s surface.
When opposite charges sufficiently accrue, the insulating ability of the air breaks down and there is a sudden and rapid discharge of electricity known as lightning. This discharge temporarily brings into balance the charged regions in the atmosphere until the opposite charges once again build up.
What is Positive Lightning ?
The lightning previously discussed is called “negative lightning”, because a negative charge is transferred from the cloud to the ground. However, lightning does not always form in the negatively charged region under the base of the thunderstorm.
Lightning can originate in the “anvil” or upper part of the cirrus clouds close to the peak of the thunderstorm, which contains highly positive charges.
According to NOAA: “Most lightning flashes are a result of negatively-charged leaders, called stepped leaders. These leaders develop downward in quick steps. Each step is typically about 50 meters (~164 ft) in length. Stepped leaders tend to branch out as they seek a connection with the positive charge on the ground. When a branch of the stepped leader reaches within about 50 meters of the ground or some object on the ground, it connects with an upward-developing positive charge, often referred to as an upward streamer.”
Lightning formed in this area of the thunderstone develops as previously described, however, the descending stepped leader is positively charged, and the ground streamers are negatively charged.
Positive lightning is rare, accounting for a mere 5% of all strikes. Even though it occurs less frequently, positive lightning is substantially more dangerous.
Since it starts in the upper levels of a storm, the amount of air through it which passes through to reach the ground is typically significantly greater. This means that electrical electric fields connected with positive Cloud-to-Ground Strikes are usually more intense than those associated with negative strikes. The flash also lasts longer with a peak induced current of up to 300,000 amperes and a potential of up to 1 billion volts !
Another thing that makes positive strike potentially more dangerous is that a strike can occur more than 25 miles away from the precipitation.
If you can hear the thunder, you are close enough to the lightning that you or a nearby object could be struck, regardless of where the storm is located according to Doppler radar.
It also believed that positive flashes are responsible for a substantial number of forest fires and damage to power lines.
What causes thunder?
The massive amount of Energy contained in a lightning bolt momentarily heats the air to approximately 50,000 degrees Fahrenheit, which is hotter than the surface of the Sun. This super-heated air explodes outward. The enormous pressure in the outgoing shock wave decreases rapidly with distance, and within ten yards or so the pressure decreases enough to be heard as what we call thunder.
Since light travels exponentially faster than sound, you can use thunder to roughly calculate the distance to the lightning strike by counting the number of seconds between the flash of lightning and the clap of thunder, then dividing by 5, you will know how many miles away the lightning is. Bear in mind you should be in a safe place while counting.
Lightning safety
Lightning is very dangerous and can cause permanent injury or death. You should always look for appropriate shelter if caught outside during a storm. This can be a building or, if you have nowhere else to go, a building or a car. If you do not have access to either one of these, then you should quickly find the lowest possible elevation, such as a valley or ravine. You should not shelter under trees or nearby metal objects. Do not gather in a group, you should spread out as far as you can.
If you are indoors, stay away from plumbing pipes (bath tub, shower). This threat has been greatly reduced with the advent of PVC (polyvinyl chloride), which is used for modern indoor plumbing. If you are unsure, err on the side of caution and avoid plumbing.
A common myth is that rubber tires are why you’re safe in a car during a lightning storm. This is simply not true. In fact, intense electrical friends can cause rubber tires to become more conductive. The reason for your safety is that lightning will travel around the surface of the vehicle and then go directly to Earth ground. In essence, your vehicle becomes what is called a Faraday cage. A British physicist, named Michael Faraday, discovered that a metal cage would protect objects within the cage that are subjected to high voltages.
For more information on lightning safety, go to: noaa.gov
