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. 2023 Dec 12;14(1):7810.
doi: 10.1038/s41467-023-42892-1.

Spectroscopy of a mesospheric ghost reveals iron emissions

María Passas-Varo  1 , Oscar Van der Velde  2 , Francisco J Gordillo-Vázquez  3 , Juan Carlos Gómez-Martín  3 , Justo Sánchez  3 , Francisco J Pérez-Invernón  3 , Rubén Sánchez-Ramírez  3 , Maya García-Comas  3 , Joan Montanyà  2
Affiliations

Spectroscopy of a mesospheric ghost reveals iron emissions

María Passas-Varo et al. Nat Commun. .

Abstract

Mesospheric Green emissions from excited Oxygen in Sprite Tops (ghosts) are infrequent and faint greenish transient luminous events that remain for hundreds of milliseconds on top of certain energetic sprites. The main hypothesis to explain this glow persistence is the long lifetime of excited atomic oxygen at 557.73 nm, a well-known emission line in aurora and airglow. However, due to the lack of spectroscopic campaigns to analyse such events to date, the species involved in the process can not yet be identified. Here we report observational results showing the temporal evolution of a ghost spectrum between 500 nm and 600 nm. Besides weak -but certain- traces of excited atomic oxygen, our results show four main contributors related to the slow decay of the glow: atomic iron and nickel, molecular nitrogen and ionic molecular oxygen. Additionally, we are able to identify traces of atomic sodium, and ionic silicon, these observations being consistent with previous direct measurements of density profiles of meteoric metals in the mesosphere and lower thermosphere. This finding calls for an upgrade of current air plasma kinetic understanding under the influence of transient luminous events.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Meteosat Second Generation infrared image (1 km resolution), showing cloud top temperatures on 21 September 2019 19:45 UTC.
Locations of lightning activity from LIghtning detection NETwork (LINET) (black dots), observation site (white circle) and the reported mesospheric ghost parent stroke (red cross) are superimposed.
Fig. 2
Fig. 2. Images recorded on 21 September 2019 at 19:45:14 UTC.
a Composite image of the jellyfish sprite (red). The slit projection is superimposed as a yellow line. Time-lapse video was taken with a monochrome Teledyne FLIR Grasshopper3 video camera (Sony IMX174 CMOS sensor) fitted with a 25 mm F0.95 lens and a 720 nm infrared long-pass filter. The exposure time of each frame was 1 s. The composite has been made using the sprite event frame as red RGB channel, the airglow image as the green channel, while the blue channel is a frame of a cirrus cloud revealed by the reflection of light from a distant lightning flash 13 s after the event. b Averaged (stacked) video frames of airglow background in the 10 s before and after the sprite time show some banded structure which we interpret as likely caused by modulation of the hydroxyl (OH*) airglow layer by gravity waves.
Fig. 3
Fig. 3. Mesospheric ghost spectrum.
a Average of the consecutive reduced spectra of the reported event from 200 ms before the sprite to 480 ms after the sprite. b, c Zoom of the emission lines of interest from 0 ms (coincident with the sprite) to 80 ms after the sprite. Grey dashed lines show the 5σ confidence threshold; grey shadowed areas show the background level ±3σ detection threshold. Thick solid horizontal bars in green, yellow and orange show the colour eye perception of the related wavelengths. We highlighted the identified forbidden emission lines with bold case labels. Asterisks show blended lines. Source data are provided as a Source Data file.
Fig. 4
Fig. 4. Line flux evolution. Right axis.
Temporal evolution of the normalised average of the line fluxes of the identified species in Table 2 (set A, black dotted line), in Table 3 (set B, black dashed line) and in Tables 2 and 3 (combined set A and set B, black solid line). Left axis: Temporal evolution of the Fe I (528.04 nm), O I (557.73 nm), N2 (560.80 nm) and Fe I (583.46 nm) line flux ratios. Note that t = 0 ms is coincident with the sprite. Source data are provided as a Source Data file.
See this image and copyright information in PMC

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