2023-12-12 18:00:22
In the mesospherea region of the atmosphere that was believed lacking electrical activity, gigantic and brief luminous flashes are produced, the discovery of which, just three decades ago, surprised the scientific community. Given his elusive characterreceived names taken from Summer night Dream (of William Shakespeare), such as ‘elves’ or ‘elves’.
Related to storm lightning, but located tens of kilometers above the clouds, among these rare events are the ‘ghosts‘ (or GHOSTs, from English GreenisH Optical emission from Sprite Tops), greenish glows whose origin was attributed to oxygen.
The ‘ghosts’ are observed in the upper region of the ‘sprites’ (goblins), a spectacular luminous event of hundredths of a second that shows a diffuse upper part and a lower region with tentacles
Now the first spectroscopic study of these events, published in the magazine Nature Communicationsassociates them with metals, such as iron or nickelwhich had never been included in optical models of mesospheric flares.
The ‘ghosts’ do not appear in isolation, but are observed in the upper region of the ‘sprites’ (goblins), a spectacular luminous event of just hundredths of a second that shows a diffuse upper part and a lower region populated by apparent tentacles (ionized air filaments between 10 and 100 meters thick).
The ‘goblins’ can extend from 40 to almost 100 kilometers above the ground and, sometimes, present a ‘greenish ghost on the diffuse upper part, which lasts hundreds of milliseconds after the disappearance of the ‘goblin’ that generated it.
A ghost (greenish flash) on a goblin. /Thomas Ashcraft.
“Since the first ‘Transient Light Events’ (or TLEs) were documented in 1989, which is how we know this family of events, people around the world have sought to capture them during the electric storms. And, in fact, he was a amateur scientist who photographed a ghost for the first time, the last discovered member of the TLE family,” points out Maria Passas Varoresearcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) who leads the work.
Until now, the main hypothesis to explain this greenish flash that appears on some more intense ‘goblins’ pointed to the interaction of charged particles (ions) with the atomic oxygen present in the atmospherea phenomenon already identified in the greenish color of the auroras. To corroborate this, the scientific team that developed this work began a systematic observation campaign in June 2019 to obtain Specters of the upper region of the ‘goblins’ (a spectrum allows us to know parameters such as temperature or composition of a celestial object).
The greenish flash is mainly due to metals such as iron and nickel, compounds that had never been taken into account when developing optical models for these events.
“One in 100 very intense goblins generates a ghost. We have analyzed more than 2,000 spectra, and only 42 corresponded to the upper ‘goblin’ region, where ‘ghosts’ usually appear. It takes a lot of luck and a lot of skill to aim the instrument at the right height, because the slit in observation It is very narrow and you have to predict where the elf is going to appear. Of the 42 spectra, only one had a sufficiently intense signal-to-noise ratio,” details Passas Varo.
That spectrum revealed, for the first time, what produces ‘ghosts’, a process in which oxygen contributes very little. The team found, instead, that the greenish glow is mainly due to metals, iron and nickel, compounds that had never been taken into account when develop optical models for TLEs.
A red goblin (indicated by the white arrow) over a storm captured by members of the Expedition 44 crew aboard the International Space Station on August 10, 2015. / NASA.
“Just that day we observed gravity waves, some atmospheric disturbances produced by intense vertical movements in the air, such as those generated by storms”, according to the author.
“We knew that in the atmosphere there are layers of metals, that come from the entrance of interstellar dustand everything indicates that these fluctuations in the density of the air make the altitude of these layers variable: thus, this variability would be responsible for the fact that the ‘ghosts’“, Explain.
The discovery of these metal atoms implies an update of the models for transient luminous events, the understanding of which is in turn fundamental to understanding how the planet’s global electrical circuit works.
REFERENCE
M. Passas et al. “Spectroscopy of a mesospheric ghost reveals iron emissions”. Nature Communications (2023)
Rights: Creative Commons.
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