With Mathilde Fontez, editor-in-chief of the scientific magazine Epsiloon, we are talking today about these lightning strikes that hit the United States and South America in 2020.
franceinfo: These flashes have just been certified as records by the World Meteorological Organization, that is to say?
Mathilde Fontez: These two storms are monsters. The first stretched over 768 kilometers. He crossed three American states: Mississippi, Louisiana, Texas. And the second, which spread to Uruguay and Argentina, also in 2020, it lasted 17 seconds. It should be remembered that a flash normally extends over a few kilometers, and it only lasts a second.
But the big news above all is that physicists have finally understood how these flashes are formed. It sounds crazy – lightning is basic, it’s a phenomenon we often see. But until then, their birth remained a scientific mystery.
WMO has verified 2 new world records for a ⚡️⚡️ #megaflash
Greatest duration of 17.1 seconds over #Uruguay and #Argentina
Longest distance of 768 km (477.2 miles) across southern #USA @NOAA imagery of US megaflash highlights advances in #satellites and detection technology pic.twitter.com/RazD75gqNM— World Meteorological Organization (@WMO) February 1, 2022
What didn’t we understand?
We did not understand where the energy that triggers the lightning comes from at the very beginning. The starting point of the whole phenomenon. So the most important. So there was an overall description, it’s the one that’s in the books: in a storm cloud, there is hail falling, and lighter ice crystals rising.
The hail rubs the crystals, it tears off their electrons: their negatively charged particles. And that’s how the bottom of the cloud becomes negatively charged, the top positively, and an electric field is formed. Except that with this mechanism, we obtain an electric field 10 times too weak to form lightning.
Physicists have been trying to figure it out for decades. But observing a thunderstorm is not so simple. The clouds are opaque. We can send balloons to probe, rockets, but they tend to trigger lightning themselves by their presence.
So what this international team did that pierced the mystery is they used telescopes: a network of thousands of telescopes that observe in radio waves, the Low Frequency Array. The advantage is that when there are clouds, telescopes are out of work for astronomy. physicists took advantage of it…
And then, what triggers the thunderbolt?
These are the ice crystals in suspension, all by themselves. Physicists have discovered that they are needle-shaped, very thin, very sharp. And that they can transform themselves into a small electric battery: by dint of bumping against each other, all their positive charges are found on one end, and all the negative charges on the other. This is how electric currents are created which are small at first, then come together and trigger the lightning.
And this mechanism has been confirmed by Covid-19. You are going to tell me that it has nothing to do, but if: the drop in pollution in the first months of the pandemic during the confinements resulted in a drop in the number of particles in the air, and therefore in a decrease in the number of crystals: the crystals in the clouds form around particles in suspension. And all this led to a 10% drop in the amount of lightning. Everything fits !