How does lightning work?

Electrical storms are one of the natural phenomena with which we are most familiar from an early age; they are so ordinary that we come to ignore all the science and processes behind them. The only thing we know is that they have a thunderous noise that scares the little ones, and that we must protect ourselves from storms, but why? I will explain this to you now.

Lightning, much more than electricity

Lightning, as you might imagine, is an electrical discharge. It behaves like those small static shocks or "sparks" that a brush can give when we brush our hair after a nap, and it makes our hair stand up; in this case, the hair is electrically charged due to rubbing, and when the brush comes close, it attracts it. The same principle applies to the formation of lightning, but on a much larger scale.

Under normal conditions, in the atmosphere there is a balance between negative and positive charges, but when an electrical storm develops, the charges inside the cloud are altered due to collisions between water and ice crystals, in such a way that positive charges accumulate at the top of the cloud and negative charges at the bottom.

Since the negative charges are in the part closest to the surface of the Earth, the objects in it are positively charged, in the same way as with the brush in the previous example; in such a way that a tension (electric potential difference) is formed between the negative charges of the cloud with the positive ones of the Earth's surface due to the attraction of the opposite charges. But there is an obstacle that prevents these charges from approaching: the air.

Air is dielectric, which means that it does not transmit electrical charges, and that in theory would prevent the charges from the cloud and the surface from meeting, but that is not what happens. The voltage that accumulates between the charges is so strong that it causes a dielectric breakdown of the air, which forms a corridor through which the charges can meet and form the luminous lightning bolt that we know. Because of this, lightning bolts are not perfect lines but appear to have branches and deviations due to the difficult breakdown of the air. And that expansion of the air causes sound waves, which we call thunder.

However, there are more ways in which lightning can form, since not all lightning reaches the ground: some forms between one cloud and another, or even within the same cloud; and others do strike the ground but start from the positive charges of the cloud, which meet negative charges on the Earth's surface. The latter are less common, but they are among the most dangerous because they strike with greater intensity.

With the intense flow of electrons through the bolt, a very hot plasma is created, which gives it the luminosity that is visible to the naked eye. The air along its path heats to about 30,000 °C, almost 5 times the temperature of the sun's surface; that is already chilling, but there is more. The luminous discharge of a lightning bolt travels at about 100,000 km/s (roughly 350 million km/h) and its power is measured in billions of watts, but the total energy of a bolt, around 1 gigajoule, is far below that of a nuclear bomb. But what scares the most is the regularity with which lightning strikes, which is approximately 44 lightning flashes per second across the entire Earth (almost 4 million a day), so in this very second that you read this, there are probably about 44 flashes happening.

With so many lightning bolts a day, it would seem very likely that you will be struck by one sometime in your life, but the figures show that the odds are about 1 in 1.2 million per year (US data) and 1 in 15,300 over a lifetime; and despite how dangerous lightning can be, only 10% of the people struck have died. But of course, the others suffered other consequences that would not be pleasant to experience either.

Normalizing the unknown

Although lightning is such a common natural phenomenon, and has been present since the Earth began, it has not yet been fully understood: it is known how it happens and what it causes, but some aspects have not been explained yet. Others that once seemed a mystery now have an explanation, such as lightning that appears when the sky is clear: these so-called "bolts from the blue" start inside a thunderstorm cloud, travel horizontally and can strike up to 10 kilometers away from it.

What is still not known exactly is why the electric charges of the clouds manage to be released in the form of lightning, since the measurements made give results of a much smaller electric field, up to 10 times less, than it should be according to theoretical models to cause such intensity and break down the air dielectrically.

Nature and all its phenomena turn out to be so complex that lightning is just one example of it; and it is in those cases that certain questions remain inexplicable to us, and all we can do is admire and try to understand them as far as possible.