Visual Range in Airborne Snow Particles

Abstract

Snow particles are large enough comparing with the wavelength of light and can be seen by eyes from a limited distance. At this point snow is different from invisible particles such as haze and fog of which radii are within several wavelengths. The mechanisms of the extinction of ligh by particles that float in the air are also different depending on their sizes. Rayleigh electromagnetic theory applies to the particles of radius very much less than wavelength and Mie theory applies to the particles of between about 0.1 and 10 times of the wavelength, however geometrical optics is applied to most of snow particles which are very large compared with the wavelength of light.
The visible snow particles leave the trail of their afterimages. It is suggested observationally and theoretically that the visible sizes and the afterimages of snow particles work on visual range shortening in snow conditions.
Poor visibility in blowing snow, which causes road clousures and traffic accidents are major concerns for the maintenance of safty road traffic. A few characteristics of visibility on road are introduced.