Spectrum of the Lightning Dart Leader

Abstract

A high-speed slitless spectrograph has been used to record photographically with 9 ?s resolution the spectral emissions from five dart leaders. All occurred in the same lightning flash which produced at least 13 return strokes. Dart leader spectral emissions in the 398-510 nm region are characterized by singlyionized nitrogen (NII) emissions. These emissions from a 13 m isolated section of the channel decrease in intensity after the passage of the dart. They are, however, continuously recorded between the dart and return stroke spectra. Three dart temperatures are calculated to be approximately 20,000 K±10%. Five dart velocities are calculated; one value (3.4?107 m s?1±20%), exceeds the highest value previously reported in the literature (2.3?107 m s?1). The relative intensity ratio of the return stroke to the dart in the isolated channel section is measured to be 8?9±15% in these data.