Of all the meteorological phenomena, our magnificent planet throws us, the lightning is one of the most spectacular – and the most mysterious. Even though storms are a common occurrence, we are still upset to understand and describe their crackling electric discharges generated in the sky.
Some kind of lightning is so strange and rare, in fact, that we didn’t even have concrete evidence that it existed until 1990, when researchers identified the “rocket-like” motion in the film filmed by NASA’s space shuttle last year.
Later called “blue jets”, the stripes are now recognized as bright flashes of light that last only a few hundred milliseconds, like lightning up in the clouds and into the stratosphere.
A blue jet photographed in Hawai’i. (Gemini Observatory / AURA / Wikimedia Commons)
We can’t easily see this phenomenon under a curtain of clouds – but that doesn’t mean that scientists can’t see it from above them. About 400 kilometers (250 miles) above the planet, it orbits the International Space Station, and for some time now, the instruments on board have been tracking these mysterious flashes of lightning upside down.
Now, after being installed in 2018, an observer for the European Space Station equipped with optical sensors, photometers and detectors for gamma and X-ray radiation recorded five blue flashes at the top of a storm cloud, one of which ended with a jet of blue streaked high into the stratosphere.
These rare observations provide valuable insight into the occurrence of mysterious discharges, according to a team of researchers led by physicist Torsten Neubert of the Technical University of Denmark.
Blue jets are considered to be triggered when a positively charged cloud peak encounters a negative charge layer at the cloud boundary and the air layer above. It is believed that this produces an electrical failure that forms a leader – an invisible conductive channel of ionized air through which lightning passes.
However, our understanding of the blue jet leader is quite limited. Here the data analyzed by Neubert and his team fill in the blanks.
On February 26, 2019, the Atmosphere-Space Interactions Monitor (ASIM) Observatory recorded five blue flashes, about 10 microseconds long each, at the top of a storm cloud, not far from the Pacific Ocean island of Nauru.
One of these flashes produced a blue jet, reaching the stratopause – the interface between the stratosphere and the ionosphere, at an altitude of about 50 to 55 kilometers (about 30 to 34 miles).
In addition, the observer recorded atmospheric phenomena called ELVES (short for light emissions and very low frequency disturbances due to electromagnetic pulse sources). These are rings with optical and ultraviolet emissions expanding into the ionosphere that appear above storm clouds, which last only a millisecond, as illustrated in the animation below.
They are thought to be generated by an electromagnetic pulse at the bottom of the ionosphere, caused by lightning discharge.
The red issue from the leader, however, was weak and very limited. This, the research team said, suggests that the leader himself is very short and localized, compared to the lightning leaders fully developed between the ground and the clouds.
This also suggests that flashes and the blue jet itself are a type of discharge streamers: branched sparks, which emit high-voltage sources, such as Tesla coils, on a chain reaction of ionizing air particles.
“We then propose that UV pulses be spirals generated by lightning currents, rather than lightning currents,” the researchers write in their paper.
Flashes, they believe, are similar to narrow bipolar events. These are high-power radio frequency discharges that occur inside clouds during storms, which are known to trigger lightning inside the cloud. The team said that the blue glows at the top of the clouds are probably the optical equivalent of this phenomenon and can turn into blue jets.
Because narrow bipolar events are quite common, this could mean that blue lightning is also more common than I thought. Knowing more about how common they are could give us a much better understanding of storms and lightning, not to mention our atmosphere and all the complex interactions in them.
The team ‘s research was published in The nature.