On October 22, 2017, a storm cloud that had accumulated over the central United States released a huge flash flood that lit up the skies of Texas, Oklahoma and Kansas,media reported. The tremor struck more than 500 kilometers across the three states on an unprecedented scale. A team of researchers has written a study on the lightning, describing it as a “megaflash”. This is one of the longest lightning strikes ever.
Generally speaking, normal lightning is between 1 and 20 kilometers long, but as mapping technology becomes more advanced, some really huge lightning is gradually coming into our sight. Recent findings raise an interesting question: How big is lightning? Should we worry about the “heavyweights” in the atmosphere?
When a strong positive charge develops in one area of a thunderstorm cloud and a strong negative charge develops in another region, an electric current is generated between them, which in turn produces lightning. Don MacGorman, a physicist and senior researcher at the National Oceanic and Atmospheric Administration (NOAA), who co-authored the 2017 “Mega Flash” study, said: “Lightning is generated in a place where electricity is very strong. They become so powerful enough that the air can no longer withstand the power of electricity, which is broken down. “
This means that as the voltage increases, the insulation of local air is destroyed. The researchers believe this is because excess electromagnetic force selves that begins to accelerate free electrons in the air (which are not attached to atoms or molecules), separating other electrons from atoms and molecules. “Scientists call this process an electronic avalanche, and that’s what we call air decomposition, ” McGorman said. “
This process eventually forms a very hot passage in the air, like a wire, with both ends extending outwards to the positive and negative charges that lead to an “electronic avalanche”. Eventually, this channel connects the positive and negative charges, which triggers a huge current, which we call lightning.
“You can think of it as a huge spark coming out of the clouds,” McGorman said. “Sometimes, there are areas of the lower clouds that usually contain positive charges, and they do not have enough charge to block the channel. As a result, the lightning continues to grow and extend downwards to the ground. When this happens, a lightning bolt with a huge current is triggered to transfer a portion of the charge of the thunderstorm cloud to the ground. When we think of lightning, most people usually think of the passages between these clouds, and the fork-like lightning strikes violently to the surface.
But what limits the scale of these giant lightning bolts?
For decades, researchers have been trying to answer that question. In the vertical direction, the range of lightning is limited by the height of the storm cloud, i.e. the distance from the ground to the apex of the cloud – up to a maximum of about 20 kilometers. But horizontally, a larger cloud system provides more space.
As early as 1956, a meteorologist named Myron Ligda proved this, using radar to detect the longest lightning bolt on record at the time, spanning 100 kilometers.
Then, in 2007, researchers broke records and found a 321-kilometer-long lightning bolt in Oklahoma. McGorman and colleagues’ recent research goes beyond that. According to the researchers, the “huge flash” they found sent an unusually strong flash, illuminating the 67,845 square kilometers of ground. However, even such lightning was surpassed by subsequent discoveries. In a recent study published in the Journal of Geophysical Research: Atmosphere, scientists described a lightning bolt spanning 673 kilometers.
Such giant lightning bolts are rare, but now we have the technology to detect them and can spot them more frequently. Scientists have relied not only on ground-based systems using antennas and radars, but on the more favorable positions of satellites to observe lightning. The two most recent record-breaking lightning bolts were measured using a technique called the Geosynchronous Lightning Mapper. The sensors are installed on two satellites orbiting the Earth, providing a wide range of images of the Earth’s storm system beneath it.
“The system reacts to the light emitted from the top of the cloud, so we can see the light emitted by lightning, and then map it, covering almost the entire hemisphere,” McGorman said. “
High-resolution satellite imagery, combined with data from the Ground Lightning Mapping Array, shows the vast range of the lightning in October 2017.
However, we still don’t know how these huge electronic light sources have grown so long. The size of the cloud is a factor, the researchers believe, because the larger the cloud system, the more likely it is that lightning will occur. McGorman added that the formation of giant lightning also requires a “mesoscale process, a large-scale airflow that allows the system to bind together for a long time.”
So what happened inside the lightning on the stage where these giant clouds were built? Christopher Emersic, of the University of Manchester in the UNITED Kingdom who studies the phenomenon of thunderstorm semory, said: “These super-large thunderstorms look like continuous discharge. “
He hypothesized that if a cloud system were highly charged over a large area, a series of discharges would pass through the area like a row of fallen dominoes. “If there is not much gap between dominoes, one triggers the other, forming a series of domino collapses. On the other hand, if a ‘failure’ is triggered, in this case you can only see a smaller space lightning event instead of a giant flash. “
The larger the mother cloud, the greater the chance that the discharge will continue to spread. “So in principle, if the charge structure is favorable, the giant flash cloud can be as big as the mother cloud, ” Emosic said. “
This also means that there may be larger lightning than has been observed so far. “Storms can be bigger than the ones we measured,” McGorman said. “In other words, we still don’t know how big the biggest lightning bolt is.
Although super-lightning is a doomsday sight, they are not necessarily more dangerous than ordinary lightning, “and a wide span of lightning doesn’t necessarily mean carrying more energy,” Explains Emosic. In addition, because the cloud systems that produce giant lightning are so large, it is difficult to predict them.
“Such events often result in ground lightning off areas far from the lightning-active areas of the convection center,” Emosic said. “
In the context of global warming, the type of storm that triggers super-flashes is also likely to increase, “so indirectly, the right conditions are more likely to form, thus increasing the frequency with which they occur,” Mr Emosic said. “
For now, however, super lightning is not common. McGorman estimates that they account for only 1% of the total lightning. But perhaps in the near future, researchers like him may find even more amazing giant lightning bolts that will make people marvel at the creation of nature.