Are you sure to know everything about lightnings? A little journey in this fascinating phenomenon

A lightning is an electrostatic discharge: a movement of electrons from a negative mass toward one charged positively. A mass, like a cloud, is negatively charged when the sum of negative charges coming from electrons exceeds the sum of positive charges coming from protons. Usually we think about a lightning as a phenomenon that happens between the clouds, where it origins, and ground. On the contrary, there are several ways for electrons to flow toward a positive mass. For instance, lightning often occurs between two clouds or within the same cloud, it can origin from the ground toward the clouds (5% of all lightning) or, intriguingly, there exists a wide range of lightning that origin from the clouds and spread toward the space.

A lightning originating from the clouds toward the ground. The most classic of lightning flows through the atmosphere at an impressive speed up to one third of light velocity, equal to 300,000 km/s (670,616,629 mph), generating a plasma column with a diameter ranging from 10 cm to 50 cm (3.97 inch to 19.65 inch) which reaches the incredible temperature of ~30,000°C (~54,500°F): about five times the temperature of the sun ~5,700°C (~10,350°F)!

We still do not know exactly the process which leads to lightning formation and precisely the priming events remain unclear. Presently the most valid theory supports the idea that the initial spark is caused by cosmic rays and gamma rays originated from most violent events in the universe. When a supernova explodes it emits radiations that travel along the universe and when one of this radiation hits a charged cloud then it primes the domino effect that generate a lightning. Thus, what we see here, on Earth, may be the result of what happened millions or billions of years ago halfway across the universe! Curiously, also lightning emits radiations in the atmosphere, and we are not talking about harmless radiations but even X-rays and gamma rays extremely dangerous for our health.

When a lightning strikes it releases ozone (O3) and nitrogen monoxide (NO). The released quantity of these two gasses are so high to be lethal within 3 m (9,80 feet) from the lightning . More, NO released during summer storms represents 90% of total quantity of gas in the atmosphere and drastically increases smog levels.

There is a lake in Venezuela, lake Maracaibo, where lightning strike for about 150-160 days, up to 280 times per hour, during a year and this lake is thought to be the place with the highest concentration of O3 in the Earth. The phenomenon is known as Maracaibo lightning, or Catatumbo lightning so named for the river which flows in the lake. The two pictures below show Maracaibo lightning phenomenon. It is the result of the winds blowing through the surrounding swamps which collect humidity and heat until they meet the mountains. Thus the ascending charged air acquires more charges, so causing massive accumulation of clouds and the following release of the charges through the lightning.

A similar phenomenon happens also in our cities, where the frequency of lightning is higher than in other areas. This happens because most of the cities are such tar and polluted islands that become warmer than the surrounding areas. The warmer air above the cities form an ascending column and the resulting frictions between air's molecules and humidity cause an accumulation of charges. As a result, frequency of lightning increases as well as the smog produced, thus contributing to warm up the cities in a loop. Among the biggest cities, Singapore has the highest rate of lightning frequency in the world.

Lightning can also occur above thunderstorm clouds, toward the space. This type of lightning has been discovered only recently in 1986 and photographed for the first time in 1989; they are rare and hard to study. For these reasons they are called sprites, or red sprites because of their colour. Accordingly to current theories, a red sprite occurs when a cloud releases the charges to the ground becoming positively charged and, in turn, attracting charges from the above masses. Usually a sprite occurs in coincidence of a strong lightning, it lasts only ten milliseconds and assumes characteristic shapes:

By means of 10,000 frame-per-second high speed camera, scientists could observe that sprites are made by clusters of ionized spheres, with a diameter ranging from 10 to 100 m (33–330 feet). Such spheres are thrown up to 80 km (50 miles) and then move downward up to 10% of the light speed, followed by a set of upward moving ionization balls. The typical red color is due to nitrogen ionized by the moving electric charges in the atmosphere. In fact the mesosphere, the layer of the atmosphere where the phenomenon occurs, is rich in nitrogen, which is indeed the most abundant gas in the atmosphere.

Blue Jets are lightning primed by similar events generating sprites. They are very similar to "normal" lightning but in this case the electric charges discharge from the upper positive region of a thundercloud toward a negative region above. For simplicity they could be considered flipped lightning and are related to usual downward lightning. As their "brothers" they can reach altitudes up to 70 km (43 miles) even if these cases are rare and they are referred as gigantic jets.