Submicrosecond Spectroscopy of Lightning‐Like Discharges: Exploring New Time Regimes. Issue 15 (7th August 2020)

• Record Type: Journal Article
• Authors: Kieu, N.; Gordillo‐Vázquez, F. J.; Passas, M.; Sánchez, J.; Pérez‐Invernón, F. J.; Luque, A.; Montanyá, J.; Christian, H.
• Is Part Of: Geophysical research letters. Volume 47:Issue 15(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-07
• Subjects: lightning -- spectroscopy -- discharges -- temperature -- high‐speed; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL088755
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Submicrosecond (0.476 μs per frame with an exposure time of 160 ns) high‐resolution (0.38 nm) time‐resolved spectra of laboratory‐produced lightning‐like electrical discharges have been recorded for the first time within the visible spectral range (645–665 nm). The spectra were recorded with the GrAnada LIghtning Ultrafast Spectrograph (GALIUS), a high‐speed imaging spectrograph recently developed for lightning research in the IAA‐CSIC. Unprecedented spectral time dynamics are explored for meter long laboratory electrical discharges produced with a 2.0 MV Marx generator. The maximum electron density and gas temperature measured in a timescale of ≤0.50 μs (160 ns) were, respectively, ≃10 18 cm −3 and ≃32, 000 K. Overpressure in the lightning‐like plasma channel, black‐body dynamics, and self‐absorption in spectral lines were investigated. Plain Language Summary: Lightning are extremely rapid and violent atmospheric electricity events taking place inside thunderclouds and between thunderclouds and the ground. Investigation of the fundamental properties of different types of lightning and lightning leaders can help to deepen our understanding on lightning propagation dynamics (stepping) and how lightning can produce high‐energy pulses of X‐ray or pulses of even higher energy (the so‐called terrestrial gamma‐ray flashes). Time‐resolved optical emission spectroscopy is an ideal diagnostic technique to remotely study the fast temporal dynamics of lightning. The fastest spectroscopic techniques used to date were able to achieve microsecond timescales. We present the first study exploring submicrosecond time regimes using the GrAnada LIghtning Ultrafast Spectrograph (GALIUS), a high‐speed imaging spectrograph recently developed for lightning research at the IAA‐CSIC. Key Points: Submicrosecond time‐resolved spectra of lightning‐like discharges are presented for the first time Some evidence points to slight non‐LTE conditions right behind the shock front in posttrigger submicrosecond times Optical thickness goes from thin (pretrigger times) to thick (submicrosecond) and back to thin (few microseconds)