A typical lightning bolt occurs as a series of charge discharges between electrically charged thunderstorm regions in the atmosphere and the Earth’s surface. A storm cloud can reach an electrical potential of millions of volts. During this natural phenomenon, which occurs on average 6,000 times every minute on Earth, thousands of amperes of electric current are generated. The temperature along the path of lightning zigzag can reach 27,760 degrees centigrade, about five times the Sun’s surface temperature.
However, since the air in which this massive charge flow takes place is not a good conductor of electricity, lightning zigzags down to the Earth’s surface instead of traveling linearly along the shortest path. This way of traveling, with many direction changes, is called a step or cascade.
Each step of the cascade is about 50 meters long. Active steps are illuminated for a millionth of a second (microsecond). When lightning reaches the end of a step, it takes about 50 microseconds for the new step to turn on. The flow of electricity in the steps is as follows: Energized electrons in the medium temporarily change the structure of some oxygen molecules, thus opening a conductive path to the lightning.
When high-energy electrons under the influence of the intense electric field in storm clouds collide with oxygen molecules, the oxygen molecules can be excited and change into a different form. This form of oxygen molecule, called delta singlet, is in a state called “intermediate stable,” meaning that the molecule will remain in this transient state for 45 minutes and then return to its lower-energy form. The delta singlet oxygen molecules formed will take electrons from the negatively charged oxygen ions around them.
For the environment to become suitable for electrical conduction, electrons must be removed above a certain level. Although it varies according to atmospheric conditions, it is sufficient for the intermediate stable oxygen form to exceed 1% to open a new step in a region. When this happens, the electric current generated during lightning is deflected towards regions with higher concentrations of delta singlet oxygen to take the lower resistance path.
Scientists believe that protecting people and structures from lightning will become increasingly important as severe weather events are on the rise as a result of global climate change. Hence the growing value of research that seeks to understand how a lightning bolt starts and how it travels.
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