Of all the weather events our magnificent planet throws at us, lightning is one of the most spectacular – and the most mysterious. Even though a storm is a regular occurrence, we are still pained to understand and describe electric hooves generated in the sky.
One type of lightning is so strange and rare, in fact, that we didn’t have solid evidence until 1990, when researchers identified their signature ‘rocket-like’ motion in last year’s video shot from NASA’s Space Shuttle.
Later dubbed the ‘Blue Jet’, the ridges are now recognized as a brilliant glow of light, which ranges up to a few hundred milliseconds, as the edge of light rises upward from the clouds and into the stratosphere.
We cannot easily see this phenomenon under the curtain of clouds – but this does not mean that scientists cannot see it from above. About 400 kilometers (250 mi) above the planet revolve the International Space Station, and for some time, instruments for these mysterious glimpses of lightning up and down have been seen.
Now, after being installed in 2018, a European Space Station Observatory is equipped with optical sensors, photometers and detectors for gamma and X-radiation, five blue flashes have been recorded from above a storm cloud, one of which is a blue jet. High in the stratosphere has ended with tremors.
According to a team of researchers led by physicist Torst Neubert at the Technical University of Denmark, these rare glimpses provide some valuable insights into the onset of mysterious discharge.
The blue jet is considered when a positively charged cloud meets a layer of negative charge at the top cloud boundary and a layer of air above. It is thought to produce an electrical breakdown that creates a leader – an invisible conductive channel of ionized air along which electricity travels.
However, our understanding of the blue jet leader is very limited. This is where the data analyzed by Neubert and his team are filling the gaps.
On 26 February 2019, the Atmosphere-Space Interaction Monitor (ASIM) Observatory recorded five blue flashes, each about 10 microseconds long, on top of a bluecloud, off the island of Nauru in the Pacific Ocean.
One of these flashes produced a blue jet, reaching the interface between the stratosphere and the ionosphere, at an altitude of about 50 to 55 kilometers (about 30 to 34 mi).
In addition, the observatory called atmospheric phenomena ELVES (low for emission of light and very low frequency disturbances due to electromagnetic pulse sources). These are expanding optical and ultraviolet emission rings in the ionosphere, visible above the storm clouds, depicted in the animation only a millisecond or so below.
They are thought to be generated by an electromagnetic pulse at the bottom of the ionosphere, due to electrical discharge.
Red emission from the leader, however, was faint and very limited. This, the research team said, suggests that the leader himself is much younger and local, compared to fully developed power leaders between the ground and the clouds.
This also suggests that the glow and the blue jet are in themselves a type of discharge streamer: sparking emitting from high voltage sources, writing sparks, like the Tesla coil, on the chain-reaction of ionizing air particles.
The researchers write in their paper, “We then propose, that UV pulses are fictitious dwarfs, which are generated by streamer flash currents, rather than electric currents.”
They glow, they believe, to be similar to narrow dipole events. These are high-power radio-frequency discharges that occur inside clouds during thunderstorms, which are known to trigger lightning within the cloud. The team said that the cloud is uppermost, the blue glow is the optical equivalent of this phenomenon, and it may develop into a blue jet.
Since narrow bipolar phenomena are fairly common, this may mean that blue flashes are also more common than we think. Knowing more about how common they are can give us a better understanding of hurricanes and lightning, not to mention our environments, and all the complex interactions in it.
The team’s research has been published in Nature.