Snow cover is the perfect example of a surface with a high albedo. It even looks like it has a high albedo by the white color and the sun light glaring off it during daylight. A high albedo means there is a significant amount of reflection. Snow cover has one of the highest albedos. It can be higher than that of clouds. The age of the snow is important in how much reflection will take place. Fresh snow has the highest albedo. Immediately after a fresh snowfall, up the 90% of the solar radiation can be reflected off the snow. It is no surprise that the surface temperature has trouble warming after a fresh snowfall. Not only is there significant reflection, but the evaporation and sublimation from the snow provide extra cooling. As snow ages it tends to get impurities mixed into the snow and the snow compacts. This allows more radiation to be able to absorb into the snow. An older snow will have an albedo of closer to around 50%. An older snow will melt way and sublimate fairly quickly in direct sunlight. The depth of the snow is important since if the sun can penetrate the snow then it will melt away faster and will reflect less sunlight. If a thin layer of snow is on for example metal and concrete surfaces the sun will be able to warm the surfaces below the snow. If the snow is thick however, there is enough reflection from the snow that the surfaces below the snow will not be able to warm up significantly. Snow cover can be seen on visible satellite imagery on a clear day since the surface snow can not hide surface features, lakes and rivers. Fresh snow cover has a very high reflection on visible imagery. On infrared imagery, snow covered areas will be cooler during the day than surrounding non-snow covered areas. On clear nights, surface snow covered areas will be cooler than they otherwise would be since snow cover is an effective emitter of longwave radiation. Often record low temperatures occur on nights with clear skies, a very cold air mass and a surface snow cover. |