Ground‐Based Observations of 337 nm and 777 nm Optical Emissions Produced by Lightning

Abstract

AbstractLightning flashes were observed in Barrancabermeja (Colombia) by two photometers centered at 337 and 777 nm wavelengths, a high‐speed camera, and the Colombia Lightning Mapping Array. Both optical and VHF radio emissions of different lightning processes are investigated. Flash initiations by upward in‐cloud breakdown present a first short optical pulse followed by a period of ∼1 kHz breakdown propagation. The ratio remains at unity or below, associated with the transition to negative horizontal leader propagation. In flash initiations by a fast‐stepped negative downward leader to ground, a dominance of the 337 nm radiance is found. Observations of downward leaders before ground strokes reveal that the luminosity measured by the photometers is dominated most of the time by the light coming from the cloud and not from the visible leader channels. One case of a visible cloud‐to‐ground channel with positive continuing current shows a high similarity in the evolution of the luminosity along the channel, 777 nm radiance, and the energy detected by the Geostationary Lightning Mapper from space. Finally, two types of recoil leaders have been observed: connecting and non‐connecting. Whereas the measured 777 nm peak radiance is similar in both types of recoil leaders, connecting recoil leaders present about seven times higher 337 nm peak radiance. Our observations generally show agreement between the VHF power and optical emissions.