Snow and Climate
Snow cover is a radiative sink. Its high short-wave albedo is combined with a high thermal emissivity which increases the amount of infrared radiation lost near the Earth's surface. The radiative losses are not replaced quickly by heat fluxes from below because of the thermal insulating properties of the snow. It is a particularly good insulator at night when radiative exchange is concentrated in the surface layers of the snow. The temperature of the snow surface may drop by > 10°C overnight, but the soil surface underlying snow cover as thin as 10 cm may drop by < 1 °C. When the melt occurs, the snow cover is a sink for latent heat because of the large amounts of energy required to change water phase. The surface energy balance is, thus, very strongly influenced by changing distributions of snow cover. Surface exchange processes are further modified by the small aerodynamic surface roughness of snow cover (typically 0.5 to 10.0 x 10-4 m) which reduces turbulence and vertical transfer. (Davies 1993)
In northern climates, snow generally begins to fall and accumulate during the late fall and early winter and melt during the late winter and spring. There is considerable variation in the amount of snow that falls, accumulates, the periods of accumulation and ablation (melting), the amount of water equivalence in the snow and the amount of snow that sublimes (evaporates directly from the crystal form into vapour). The layer of accumulated snow behaves in a number of ways which affects climate. Snow reflects more sunlight than soils and snow acts as an insulator which keeps the soil from cooling. Snow acts as a water source that is released in the spring.
Snow cover is a radiative sink. Its high short-wave albedo is combined with a high thermal emissivity which increases the amount of infrared radiation lost near the Earth's surface. The radiative losses are not replaced quickly by heat fluxes from below because of the thermal insulating properties of the snow. It is a particularly good insulator at night when radiative exchange is concentrated in the surface layers of the snow. The temperature of the snow surface may drop by > 10°C overnight, but the soil surface underlying snow cover as thin as 10 cm may drop by < 1 °C. When the melt occurs, the snow cover is a sink for latent heat because of the large amounts of energy required to change water phase. The surface energy balance is, thus, very strongly influenced by changing distributions of snow cover. Surface exchange processes are further modified by the small aerodynamic surface roughness of snow cover (typically 0.5 to 10.0 x 10-4 m) which reduces turbulence and vertical transfer. (Davies 1993)
In northern climates, snow generally begins to fall and accumulate during the late fall and early winter and melt during the late winter and spring. There is considerable variation in the amount of snow that falls, accumulates, the periods of accumulation and ablation (melting), the amount of water equivalence in the snow and the amount of snow that sublimes (evaporates directly from the crystal form into vapour). The layer of accumulated snow behaves in a number of ways which affects climate. Snow reflects more sunlight than soils and snow acts as an insulator which keeps the soil from cooling. Snow acts as a water source that is released in the spring.