Lightning spectra in the 850‐ to 1400‐nm near‐infrared region

Abstract

Lightning spectra in the 850‐ to 1400‐nm near‐infrared region have been recorded with 200‐ to 300‐ms time resolution using a slitless spectrometer with a lead sulfide detector. Except for the wire portion of triggered discharge channels, rocket triggered and natural return stroke spectra are very similar. The following neutral atomic nitrogen (NI) and oxygen (OI) multiplet emissions have been identified (the wavelength, in nanometers, of the brightest line in each group is shown in parentheses): NI(2) (821.6), OI(4) (844.6), NI(1) (868.0), NI(15) (906.1), OI(8) (926.6), NI(7) (939.3), NI(19) (986.2), NI(18) (1011.3), NI(28) (1053.9), and NI(36) (1246.8). Continuum emissions with peak intensities at least an order of magnitude less than the strongest line emissions were detected. A laboratory arc simulation of a return stroke discharge produced a near‐IR spectrum containing all the features emitted by lightning. Additional NI radiation peaks at 1131.4 nm (NI(17)) and 1358.1 nm on the arc spectra overlapped water vapor absorption bands and were not visible on lightning spectra recorded at 2.2‐km range. A time‐averaged lightning channel temperature of about 16,000°K was calculated from the ratio of relative intensities of the NI(1) and NI(18) multiplets.