Everyone saw the lightning and marveled at its power. But despite its frequency – about 8.6 million lightning strikes occur worldwide every day – why lightning travels several steps from the thundercloud to the base has been a mystery.
There are several books about lightning, but no one has explained how the “zigzag” (called steps) are formed, and how the lightning travels for many kilometers.
My new research provides an explanation.
The strong electric field in a thunderstorm excites electrons to enough energy to form what are known as “singlet delta oxygen molecules”.
These molecules and electrons slowly build up to form a short, spectacular beam, which glows brightly for just one minute of a second.
At the end of this step, there is a pause as the construction resumes, followed by another bright, shiny jump. This process is repeated over and over again.
The increase in weather events means that lightning protection is more important. Knowing how a lightning strike starts means we can know how to best protect buildings, airplanes, and people.
Also, although the use of non-environmental materials in aircraft improves fuel efficiency, these materials increase the risk of lightning damage, so we must look for additional protection.
What causes a lightning strike?
Lightning strikes occur when thunder clouds with an electrical current of millions of volts are connected to the earth. Thousands of amps of heat travel between the ground and the atmosphere, with temperatures of tens of thousands of degrees.
Images of lightning show information that is not visible to the naked eye. There are usually four or five weak “leaders” coming out of the cloud. These are the branches and zigzags on the unstable road to the world.
The first of these leaders to reach the earth causes the lightning. Then the other leaders are turned off.
Fifty years ago, high-speed photography revealed a serious problem. The leaders descend from the cloud in “steps” about 50 meters (164 feet) high. Each step lights up for only one minute of one second, but there is total darkness.
After 50 millionths of a second it is reproduced, at the end of the previous step, but the previous steps remain dark.
Why are there such methods? What happens in the dark moments between the steps? How can stairs be connected to the cloud without a visible connection?
The answers to these questions lie in understanding what happens when an energetic electron hits an oxygen molecule.
If the electron has enough energy, it excites the molecule into a singlet delta state. It has a “metastable” state, meaning it’s not very stable – but it usually doesn’t fall into low power for 45 minutes or so.
The oxygen in this singlet delta region removes electrons (which are needed for electricity to flow) from the oxygen-free ions. These ions are immediately replaced by electrons (which carry a negative charge) and bind to oxygen molecules.
When more than 1 percent of the air is in the atmosphere, the air can conduct electricity.
Therefore, lightning strikes occur because enough neutral space is created to remove more electrons. In the dark phase of the step, the density of metastable states and electrons increases.
After 50 millionths of a second, the step can conduct electricity – and the voltage at the end of the step increases to almost a cloud, and it creates another step.
The excited molecules created in the previous steps form a column to the cloud. The entire unit is powered by electricity, requiring no electrical space and low light output.
Protecting people and property
An understanding of lightning patterns is important in designing the protection of buildings, aircraft, and people.
Although it is rare for people to be struck by lightning, buildings are often struck – especially tall and distant ones.
When lightning strikes a tree, water pours into the tree and the resulting steam makes the trunk stronger.
Similarly, when lightning strikes the corner of a building, the rainwater that seeps into the concrete boils. The pressure explodes in every corner of the building, causing a fatal accident.
The lightning rod invented by Benjamin Franklin in 1752 is basically a thick wire that is attached to the top of a house and attached to the ground. It is designed to attract lightning and the earth’s electrical energy. By guiding the flow through the wire, it saves the house from damage.
These Franklin rods are a must for skyscrapers and churches today, but what is not known is how many are needed for each building.
In addition, hundreds of buildings are not protected, including parks. These buildings are often made from highly conductive steel, which attracts lightning, and are supported by wooden poles.
The new version of Standards Australia for lightning protection recommends that such shelters be made.
John Lowke, Adjunct Research Professor of Physics, University of South Australia
This article is reprinted from The Conversation under a Creative Commons license. Read the first article.