Colored thunderstorms.

Abstract

Three scenarios that produce colored thunderstorms are simulated. In Scenario #1, the thunderstorm's sunlit face exhibits a color gradient from white or yellow at top to red at base when the sun is near the horizon. It is simulated with a second-order scattering model as a combination of sunlight and skylight reflected from the cloud face that is attenuated and reddened by Rayleigh and Mie scattering over the long optical path near sunset that increases from cloud top to base. In Scenario #2, the base of the precipitation shaft appears luminous green-blue when surrounded by a much darker arcus cloud. It is simulated as multiply scattered light transmitted through the precipitation shaft using a Monte Carlo model that includes absorption by liquid water and ice. The color occurs over a wide range of solar zenith angles with large liquid water content, but the precipitation shaft is only bright when hydrometeors are large. Attenuation of the light by Rayleigh and Mie scattering outside the precipitation shaft shifts the spectrum to green when viewed from a distance of several kilometers. In Scenario #3, the shaded cloud face exhibits a "sickly" yellow-green color. It is simulated with a second-order scattering model as the result of distant skylight that originates in the sunlit region beyond an opaque anvil of order 40 km wide but is attenuated by Rayleigh and Mie scattering in its path to the cloud and observer.