NIGHTTIME OBSERVATIONS OF THUNDERSTORM ELECTRICAL-ACTIVITY FROM A HIGH-ALTITUDE AIRPLANE
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abstract
Two sets of observations from a NASA U-2 airplane flying at approximately 20 km altitude over nocturnal thunderstorms are reported. Photographs show frequent lightning activity in the upper part of the cloud. In some cases, only the diffuse illumination produced by the lightning can be seen. In other cases unobscured segments of lightning channels 1 km or longer are visible in clear air around and above the cloud. Multiple images of lightning channels, accidentally displaced on the film during transport of the film in the camera, indicate multiple discharges in the same channel. Photographs taken through a diffraction grating show that the lightning has a spectrum similar to that which has been observed in the lower troposphere. Lightning spectra obtained with a slitless line-scan spectrometer show strong singly ionized nitrogen emissions at 463. 0 and 500. 5 nm. Field changes measured with an electric field-change meter correlate with pulses measured with a photocell optical system. It has been found unexpectedly that a multitude of weak lightning channels commonly exists in the clear air above or around cloud tops. This indicates that lightning is capable of introducing chemical species, ions, and space charge directly into the upper troposphere and lower stratosphere.
