Abstract

Green thunderstorms are observed occasionally. Only the severest thunderstorms are green. With one exception, they have received no scientific attention, experimental or theoretical. Fraser suggested that a thick thunderstorm provides a dark backdrop. Greenness is a consequence of reddened sunlight illuminating selective scatterers along the observer’s line of sight. Thus a thunderstorm is not green, it is a black backdrop for green airlight near sundown. An alternative explanation, more in accord with my observations, is that green thunderstorms may be a consequence of the intrinsic blueness of clouds because of absorption by pure water, liquid or ice. Most clouds are so thin that the light transmitted by them is not markedly colored because of absorption. Only the most massive clouds, large both vertically and horizontally, are thick enough to color incident sunlight upon transmission. If that incident light is reddened, the transmitted light can be perceptually green.

© 1992 Optical Society of America