2024-01-20 20:14:37
The words ‘ghost’, ‘goblin’, ‘elf’ or ‘giant’ are associated with luminous atmospheric phenomena that are created on stormy nights. They invariably lead us to think of characters from fantastic literature, unrelated to science. However, these terms are also used to identify short-lived, luminous natural phenomena that occur on certain stormy nights. These phenomena, known as Transient Light Events (TLE), arise alongside the flash of light produced by lightning, which breaks the air and traces its sinuous path in the sky. At these times, in the highest part of the clouds, scientists have observed faint flashes of light known as ‘Sprites’, faint expanding disks of light called ‘Elves’, jets of blue light called ‘Blue Jets’ ‘ and structures that extend upwards, known as ‘Giants’. Among all of these, there is a very faint and difficult to observe phenomenon that remains for a few milliseconds above certain energetic sprites, which they have called ‘Ghost’.
The first observation of a mesospheric ghost occurred in May 2019 when a citizen scientist was trying to capture the presence of sprites in a storm over the Oklahoma sky. When analyzing the images obtained, he realized that a greenish glow that lasted several milliseconds appeared above certain goblins. This new phenomenon received its name from the acronym Green emissions from excited Oxygen in Sprite Tops (ghost), because, until now, the main hypothesis to explain its greenish color was that it is generated by excited oxygen atoms.
After this discovery, a team of researchers, including our guest on Talking with Scientists, María Passas Varo, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC), began a campaign aimed at obtaining spectra of mesospheric ghosts in order to to better understand the chemistry and dynamics of these ghosts.
Since June 2019, the team recorded the images and spectra of 42 sprites. Of these 42 events, only one, captured on September 21, 2019 over a storm cell developing over the Mediterranean Sea, could be classified as a mesospheric ghost.
The spectrum of the mesospheric ghost showed not only trace oxygen ions, but also the presence of iron, nickel, nitrogen, and traces of sodium and silicon. These elements are compatible with the remains left by meteoroids that impact the atmosphere from outer space to Earth.
The results have been published in the journal Nature Communications in an article signed by María Passas and her colleagues.
In conclusion, mesospheric ghosts are not only an impressive and difficult to capture visual spectacle, but also a window to the understanding of complex and dynamic atmospheric processes. Through studies like these, researchers continue to unravel the mysteries of our atmosphere and expand our knowledge about the world we live in.
We invite you to listen to María Passas Varo, telecommunications engineer and researcher in the Solar System Department of the Institute of Astrophysics of Andalusia (IAA-CSIC).
References:
Passas-Varo, M., Van der Velde, O., Gordillo-Vázquez, FJ et al. Spectroscopy of a mesospheric ghost reveals iron emissions. Nat Comuna 14, 7810 (2023).
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