Abstract
AbstractHigh speed spectra (between ∼380 nm and ∼800 nm) of meter‐long lightning‐like discharges recorded at 672,000 fps and 1,400,000 fps (with 1.488 and 0.714 μs time resolutions and 160 ns exposure time) show optical emissions of neutral hydrogen, singly ionized nitrogen, oxygen, and doubly ionized nitrogen which are similar to those found in natural lightning optical emissions. The spectra recorded in the near ultraviolet‐blue range (380–450 nm) and visible‐near infrared (475–793 nm) exhibited features of optical emissions corresponding to several molecular species (and emission bands) like cyanide radical (CN) (Violet bands), N2 (Second Positive System), N2+ (first negative system), C2 (Swan band) and CO (Quintet and Ångström bands). Molecular species can be formed at regions of the lightning‐like channel where the gas temperature would be milder and/or in the corona sheath surrounding the heated channel. We have quantified and compared electron densities and temperatures derived from different sets of neutral and ion line emissions and have found different sensitivities depending on the lines used. Temperatures derived from ion emissions are higher and change faster than those derived from neutral emissions.
Highlights
Details of lightning spectroscopy studies in the first half of the twentieth century have been reviewed by Salanave (1961)
Our study explores the presence of molecular species production in heated lightning-like channels by using a forefront detector for microsecond and sub-microsecond time resolved lightning spectroscopy
Electron densities obtained from the Full Width at Half Area (FWHA) of the Stark broadened Hα line in the visible-near infrared spectra recorded at 672000 fps are shown in figure 6(a) and 6(b) for ∼ 1 meter long sparks in the Switching Impulse (SI) and Lightning Impulse (LI) modes, respectively
Summary
Physik der Atmosphäre, Oberpfaffenhofen, High speed (down to submicrosecond time scales), high sensitivity lightning-like spectra (380 nm-800 nm) reveal a rich chemistry. Molecular species like CO, CN, C2 , N2 and N2 + are detected. This opens the door to find and quantify lightning NO production by spectroscopy. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record.
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