[--MAIN HOME--] [--ALL HABYHINTS--] [--FACEBOOK PAGE--] SOLAR INTENSITY AND SNOW SUBLIMATION METEOROLOGIST JEFF HABY Even when the temperature is below freezing, surface snow cover will gradually reduce over time if no additional snow or moisture precipitates or accumulates on the ground. Ice can go straight from an ice to a vapor. This is called sublimation. Sublimation is fairly slow since it takes quite a bit of energy for an ice molecule to escape the solid rigid structure and escape to a gas. Sublimation will be enhanced under direct sunlight since photons of solar energy will add the energy necessary for solid ice molecules to escape. The relationship between sun angle and solar intensity is such that as the sun angle increases above the horizon the solar intensity at the surface increases at an increasing rate. Therefore higher sun angles are much better at surface snow sublimation than lower sun angles. Sublimation will occur even at the low sun angles but the amount of sublimation is very weak. At very low sun angles the reflection of solar energy off the snow surface is a very high percentage, the sun has to travel through a longer fetch of the atmosphere thus weakening the solar intensity, the sinusoidal relationship between sun angle and solar intensity results in weak solar intensity at a low sun angle, and shadow casting on the earth's surface reduces much of the sunlight that strikes the surface. The higher the sun angle gets the weaker the four effects mentioned previously are. These effects weaken at a more rapid rate for each degree higher the sun angle becomes. Since sun angle is a minimum at the start of winter and much higher in late winter, the sublimation power of the sun on surface snow will be much higher in late winter as compared to early winter on sunny days.