Spanish astronomers for the first time carried out a spectroscopic analysis of a rare atmospheric phenomenon known as “ghosts“. This is stated in a new study published in the journal Nature Communications. The study was carried out by employees of the Institute of Astrophysics of Andalusia and the Polytechnic University of Catalonia.
The phenomenon of “ghosts” is a form of short-term luminous events (TLE) that arise above thunderstorms in the upper layers of the atmosphere. These phenomena, first discovered in 1989, include lightning “sprites”, as well as Galo, elves, blue jets, and giant streams.
In 2019, during a storm observation in Oklahoma, an unusual green glow was recorded, which lasted several milliseconds, over energetic sprites. This phenomenon is probably caused by the excitation of oxygen in the upper parts of the sprites, and was called “green radiation of excited oxygen in the upper parts of the sprites” or unofficially, “ghosts”.
Researchers, led by Maria Passas-Varo, initiated a systematic spectroscopic study to analyze the spectral radiation of “ghosts”. The goal was to study the temporary evolution of spectral radiation in the range from 500 to 600 nm.
The team found that atomic oxygen excited by about 557.73 Nm plays a key role in this phenomenon. This radiation line is also present in polar radiance and other atmospheric phenomena. In addition, traces of atomic sodium, ionized silicon, molecular nitrogen, as well as atomic nickel and iron were discovered in the spectra of the “ghosts”, and atomic nickel and iron.
Of particular interest is the greenish glow of the “ghosts”, which, according to scientists, may be associated with excited neutral iron at the wavelengths of 580.45 nm, 583.46 Nm, and 586.72 nm. These radiations can be recorded by the green component of most cameras.
The results of the study may require a review of existing theories about these atmospheric phenomena and the development of more accurate models of plasma kinetics and electrodynamics in conditions of TLE.